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English–Turkish space glossary

Short, clear definitions of the terms used in astronomy, space science, rocketry, satellites and aviation, with their Turkish equivalents. Search for a term you met in the news or a paper, browse by letter or filter by topic.

In the glossary

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Every term has its Turkish equivalent and a definition; related terms link to a detailed page on the site.

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21-centimeter line (hydrogen line) 21 cm çizgisi (hidrojen çizgisi)

Radio emission at 1420 MHz produced when the spins of the electron and proton in a neutral hydrogen atom flip relative to each other. It is a key tool for mapping gas in galaxies.

21-centimetre hydrogen line 21 cm hidrojen çizgisi

A radio emission line from neutral hydrogen atoms at a frequency of 1420.4 MHz. It is used to map the distribution and motion of cold gas in galaxies.

25-year rule 25 yıl kuralı

An international guideline that low-orbit satellites should leave orbit within 25 years of mission end; some regulators have since shortened the period.

51 Pegasi b 51 Pegasi b

The first exoplanet discovered around a Sun-like star, found by Michel Mayor and Didier Queloz in 1995, a feat honoured with the 2019 Nobel Prize in Physics.

67P/Churyumov–Gerasimenko 67P/Churyumov–Gerasimenko

A two-lobed short-period comet that ESA's Rosetta orbited from 2014 to 2016. Its Philae lander touched down in November 2014, the first landing on a comet.

99942 Apophis Apophis

An asteroid about 340 metres across that will pass roughly 32,000 km from Earth's surface on 13 April 2029, closer than geostationary satellites, with no risk of impact.

ʻOumuamua (1I/2017 U1) ʻOumuamua

Discovered in October 2017, the first object confirmed to be passing through the Solar System from interstellar space. It drew attention for showing no obvious coma and its apparently elongated shape.

Abiogenesis Abiyogenez

The emergence of life from non-living chemistry through natural processes, the subject of research into how life began on Earth.

Ablative cooling Ablatif soğutma

A method in which a special lining in the chamber or nozzle slowly chars and erodes, carrying heat away as it does. It is common in solid motors and expendable nozzles.

Ablative heat shield Ablatif ısı kalkanı

A heat shield whose surface chars and erodes as it heats, carrying heat away from the vehicle. AVCOAT flew on Apollo and Orion, and PICA variants on Stardust and Dragon.

Abort Acil durdurma

Ending a mission when a serious failure occurs during launch or flight and bringing the crew to safety; in 2018 the Soyuz MS-10 crew survived this way.

Absolute magnitude Mutlak kadir

The brightness a star would have if seen from 10 parsecs, removing the effect of distance so intrinsic luminosities can be compared; the Sun's is about +4.8.

Absorption line Soğurma çizgisi

A dark line on a continuous spectrum, produced when cooler gas in the light's path absorbs specific wavelengths. Most lines in stellar spectra are of this kind.

Accelerating expansion Hızlanan genişleme

The finding that the universe's expansion is speeding up over time. It was discovered in 1998 using Type Ia supernovae and earned the 2011 Nobel Prize in Physics.

Accretion disk Yığılma diski (toplanma diski)

A disk of gas and dust orbiting a star, neutron star or black hole while slowly spiraling inward. Friction heats it, and it often radiates intensely.

Achromatic lens (achromat) Akromatik mercek

A lens made of two elements of different glass types that brings two wavelengths to the same focus, greatly reducing chromatic aberration.

Active debris removal (ADR) Aktif çöp temizleme

Capturing large, hazardous pieces of orbital debris with dedicated spacecraft and removing them from orbit or moving them to a safe region.

Active galactic nucleus (AGN) Aktif galaksi çekirdeği

A galaxy centre that can outshine its whole host because matter is falling onto its supermassive black hole. It radiates strongly across the spectrum, from radio waves to gamma rays.

Active optics Etkin optik

A system that uses actuators behind a large telescope mirror to correct, at a slower pace, distortions caused by gravity, temperature and wind.

Active sensor Aktif algılayıcı

A sensor that sends out its own energy and measures what bounces back, such as radar or lidar. It needs no sunlight and can work at night.

Adaptive optics (AO) Uyarlanır optik

Technology that corrects blurring from atmospheric turbulence in real time using a flexible mirror whose shape is adjusted hundreds of times per second.

Aerobraking Atmosferik frenleme

Repeatedly dipping an orbiter's lowest point through the upper atmosphere so drag slows it, shrinking the orbit without spending fuel. It has been used often at Mars.

Aerodynamics Aerodinamik

The branch of fluid mechanics that studies how air moves and the forces it exerts on bodies travelling through it; it underpins the design of aircraft, rockets and cars.

Afterburner (reheat) Art yakıcı

A system that injects and burns extra fuel in the exhaust downstream of the turbine to boost thrust sharply for short periods; mostly used on fighters because of its heavy fuel use.

Age of the universe Evrenin yaşı

The time elapsed since the Big Bang, about 13.8 billion years according to Planck satellite data. It is calculated from the Hubble constant and the universe's contents.

AGN feedback AGN geri beslemesi

The process by which energy and winds from a central black hole heat and expel a galaxy's gas, regulating or suppressing star formation.

Aileron Kanatçık (aileron)

Control surfaces on the outer trailing edges of the wings that move in opposite directions to roll the aircraft.

Air traffic control (ATC) Hava trafik kontrolü

A ground-based service that issues instructions and information to pilots to keep aircraft safely separated and traffic flowing in an orderly, efficient way.

Airfoil Kanat profili

The cross-sectional shape of a wing, propeller blade or rotor blade, usually with a rounded front and a sharp rear edge, designed to generate lift efficiently.

Airlock Hava kilidi

A chamber that can be emptied and refilled with air, allowing passage between a pressurized interior and the vacuum outside; astronauts begin spacewalks from it.

Airmass Hava kütlesi

The thickness of atmosphere light passes through, relative to the thickness at the zenith. It is 1 straight overhead and about 2 at 30 degrees above the horizon.

Airspeed indicator Hava hızı göstergesi

A primary flight instrument that uses the difference between pitot and static pressure to display the aircraft's speed through the air, usually in knots.

Airy disk Airy diski

The bright central spot, ringed by faint fringes, that diffraction makes of a point-like star in a perfect optical system. Its size shrinks as aperture grows.

al-Biruni Bîrûnî

A 10th–11th-century polymath who wrote on astronomy, mathematics and geography and calculated Earth's radius from a mountain's height and the dip of the horizon.

Algol (Demon Star) Algol (Şeytan Yıldızı)

An eclipsing binary in Perseus that dims noticeably every 2.87 days or so. Its name comes from an Arabic phrase meaning "the demon's head".

Alpha Centauri Alfa Centauri

The nearest star system to the Sun, in Centaurus about 4.4 light-years away. It consists of the Sun-like stars A and B and the red dwarf Proxima Centauri.

Altazimuth mount Altazimut kundak

A simple mount that moves a telescope up and down in altitude and left and right in azimuth. Dobsonians and many giant observatory telescopes use it.

Altimeter Altimetre

An instrument showing an aircraft's height; a barometric altimeter measures outside air pressure, while a radar altimeter uses radio waves to find the true distance to the ground.

Altitude (elevation) Yükseklik açısı

The angular height of an object measured upward from the horizon, from 0° at the horizon to 90° at the zenith.

Ammonium perchlorate composite propellant (APCP) Amonyum perkloratlı kompozit yakıt

The most common solid rocket propellant, combining ammonium perchlorate as oxidizer, aluminium powder as fuel and a polymer binder. Most large boosters and missiles use it.

Analog mission Analog görev

A study that reproduces the isolation and constraints of a space mission on Earth; in the Mars-500 experiment, six people spent 520 days in a sealed facility.

Andromeda Galaxy (M31) Andromeda Galaksisi

The nearest large spiral galaxy to the Milky Way, about 2.5 million light-years away. One of the most distant objects visible to the naked eye, it is moving towards us.

Angle of attack (AoA) Hücum açısı

The angle between a wing's chord line and the oncoming airflow; lift rises as it increases until a critical value, beyond which the flow separates and the wing stalls.

Angular diameter Açısal çap

The angle an object spans on the sky as seen by the observer, depending on both its true size and distance; the Sun and Moon each appear about half a degree across.

Antenna gain Anten kazancı

A measure of how strongly an antenna concentrates energy in a given direction compared with an ideal antenna radiating equally in all directions, expressed in dBi.

Anti-satellite weapon (ASAT) Uydusavar silah (ASAT)

A weapon designed to disable or destroy satellites; direct-hit tests such as China's in 2007 and Russia's in 2021 created thousands of pieces of debris.

Aperture Açıklık (apertür)

The diameter of a telescope's main light-collecting lens or mirror. Larger aperture gathers more light and resolves finer detail, making it a telescope's most important specification.

Aperture photometry Diyafram fotometrisi

Measuring a star's brightness by summing the light within a circle drawn around it in an image and subtracting the surrounding sky background.

Aperture synthesis Açıklık sentezi

Building an image equivalent to a large virtual aperture by combining measurements from antenna pairs in an interferometer array, aided by Earth's rotation.

Aphelion Günöte

The point in an orbit around the Sun where a body is farthest from the Sun; Earth passes aphelion in early July each year.

Apoapsis (apoapse) Apoapsis (enuzak nokta)

The point in an orbit where the body is farthest from the central mass and moves slowest; it is called apogee around Earth and aphelion around the Sun.

Apochromatic lens (apochromat) Apokromatik mercek

A high-quality lens that uses special low-dispersion glass to bring three wavelengths to a common focus, almost eliminating chromatic aberration. It is popular for astrophotography.

Apogee Yeröte (apoje)

The point in the orbit of the Moon or a satellite where it is farthest from Earth; the engine burn that circularises a geostationary orbit is usually made here.

Apollo 13 Apollo 13

The 1970 mission whose Moon landing was called off after an oxygen tank exploded; the crew survived by using the lunar module as a lifeboat and returned safely.

Apollo asteroids Apollo asteroitleri

Near-Earth asteroids whose orbits are larger than Earth's on average but whose closest point to the Sun dips inside Earth's orbit, so they cross it. They form the largest known group.

Apollo lunar samples Apollo Ay örnekleri

The roughly 382 kg of rock and regolith brought back from the Moon by six Apollo missions between 1969 and 1972. They underpin much of what we know about the Moon's age and origin.

Apollo programme Apollo programı

NASA's lunar programme of 1961–1972; across six successful landing missions, twelve astronauts walked on the surface of the Moon.

Apollo–Soyuz Test Project Apollo–Soyuz Test Projesi

The first joint crewed mission of the US and the Soviet Union, in which an Apollo capsule and a Soyuz spacecraft docked in orbit in 1975.

Apophis Apophis

A near-Earth asteroid about 340 m across. On 13 April 2029 it will pass harmlessly about 32,000 km above Earth's surface, inside the orbits of geostationary satellites.

Apparent magnitude Görünür kadir

The brightness of an object as seen from Earth; Sirius is about −1.46, while the faintest naked-eye stars under dark skies are around +6.

Apsidal precession (perihelion precession) Apsis presesyonu (günberi kayması)

The slow rotation of an orbit's long axis in space; general relativity explained the extra shift of about 43 arcseconds per century in Mercury's perihelion.

Arcsecond (arcsec) Yay saniyesi

A unit of angle equal to 1/3600 of a degree, or 1/60 of an arcminute; stellar parallaxes and telescope resolution are usually quoted in it.

Argument of periapsis Günberi argümanı (periapsis argümanı)

The angle measured within the orbital plane from the ascending node to the point of periapsis; it sets the orientation of the ellipse within its plane.

Ariane 6 Ariane 6

The European Space Agency's successor to Ariane 5, which first flew in July 2024. It uses a Vulcain 2.1 on the core stage and a restartable Vinci engine on the upper stage.

Armed unmanned aerial vehicle (armed UAV) Silahlı insansız hava aracı (SİHA)

An unmanned aircraft able to carry and release guided munitions as well as conduct surveillance; Turkey's Bayraktar TB2 and ANKA-S are well-known examples.

Arrokoth Arrokoth

A two-lobed Kuiper belt object that New Horizons flew past on 1 January 2019. It is the most distant object ever explored up close by a spacecraft.

Artemis Accords Artemis Mutabakatı

A non-binding multilateral set of principles, launched by the United States in 2020, on transparency, interoperability and resource use in civil exploration of the Moon and beyond.

Artemis programme Artemis programı

A NASA-led international programme to return people to the Moon, this time to its south polar region, and establish a lasting presence; it is also seen as a step towards Mars.

Artificial gravity Yapay kütleçekim

Creating a sense of weight by spinning a spacecraft or habitat so that centripetal acceleration presses occupants outward; it is proposed as a remedy for microgravity's health effects.

Artificial satellite Yapay uydu

A human-made object placed in orbit around a celestial body. The first was Sputnik 1, launched on 4 October 1957.

Aspect ratio Açıklık oranı

The square of the wingspan divided by the wing area; it is high on long, slender wings such as those of gliders and reduces induced drag.

Asteroid (minor planet) Asteroit (küçük gezegen)

A rocky or metallic body orbiting the Sun that is far smaller than a planet. Sizes range from a few metres to hundreds of kilometres across.

Asteroid belt (main belt) Asteroit kuşağı (ana kuşak)

The region between the orbits of Mars and Jupiter, about 2.1–3.3 AU from the Sun, where most asteroids are found. Its total mass is only a small fraction of the Moon's.

Astrobiology Astrobiyoloji

The interdisciplinary science that combines biology, chemistry, geology and astronomy to study the origin, evolution, distribution and future of life in the universe.

Astrodynamics (orbital mechanics) Astrodinamik (yörünge mekaniği)

Celestial mechanics applied to spacecraft, covering mission calculations such as trajectory design, manoeuvres, transfer orbits and launch windows.

Astrolabe Usturlap

A brass observing and computing instrument based on a flat projection of the celestial sphere, used to measure star and Sun altitudes to find time, latitude and the qibla.

Astrometry Astrometri

The branch of astronomy that precisely measures the positions, distances and motions of celestial objects. The Gaia mission has reached microarcsecond-level accuracy in this field.

Astronaut Astronot

A person trained to serve as a crew member aboard a spacecraft; the word is used especially for space travellers of the US, European, Japanese and Canadian agencies.

Astronaut candidate Astronot adayı

A person who has been selected and begun basic training but has not yet qualified for flight assignment; at NASA this phase takes about two years.

Astronaut selection Astronot seçimi

The multi-stage process in which space agencies pick candidates from thousands of applicants based on education, health, psychological resilience and teamwork.

Astronaut training Astronot eğitimi

An intensive preparation programme, often lasting years, covering spacecraft systems, robotics, spacewalks, survival, languages and medical skills before a mission.

Astronomical seeing Görüş (seeing)

How much atmospheric turbulence blurs and shimmers star images. It is measured as the width of a star image in arcseconds, and is below one arcsecond at the best sites.

Astronomical unit (au) Astronomik birim (AB)

A unit of length roughly equal to the mean Earth–Sun distance, defined since 2012 as exactly 149,597,870,700 metres.

Astronomy Astronomi (gökbilim)

The science that studies celestial objects, their motions and physical nature, and the universe as a whole through observation and theory; one of the oldest natural sciences.

Astrophotography Astrofotoğrafçılık

Photographing celestial objects and the night sky. It ranges from wide-angle Milky Way shots to long-exposure telescopic imaging of nebulae and planets.

Asymptotic giant branch (AGB) Asimptotik dev kolu (AGB)

The final giant phase of low- and intermediate-mass stars, in which helium and hydrogen burn in two shells around a carbon-oxygen core. The star loses much of its mass during this stage.

Atmospheric extinction Atmosferik sönümleme

The dimming of starlight by scattering and absorption in the atmosphere. It increases toward the horizon, making objects look fainter and redder.

Atmospheric reentry Atmosfere yeniden giriş

A spacecraft or stage entering the atmosphere from space at high speed. The intense heating comes mainly from compressing the air ahead of it, not friction; orbital return speed is about 7.8 km/s.

Atmospheric window Atmosferik pencere

Wavelength ranges in which Earth's atmosphere lets radiation through. The main ones are visible light, some infrared bands and the radio window; other wavelengths require space telescopes.

Attitude Tutum

A spacecraft's orientation in space, meaning how its axes are rotated relative to a reference frame. Pointing antennas at Earth and panels at the Sun depends on it.

Attitude determination and control subsystem (ADCS) Tutum belirleme ve kontrol alt sistemi

The subsystem that measures a spacecraft's orientation with sensors and turns it to the desired direction with actuators. Star trackers, gyroscopes, reaction wheels and magnetorquers are typical parts.

Attitude indicator (artificial horizon) Yapay ufuk

A gyroscopic instrument showing the aircraft's pitch and bank relative to the real horizon; it is the cornerstone of instrument flying in cloud and at night.

Aurora Kutup ışığı (aurora)

Curtains of green, red and violet light produced when solar charged particles excite oxygen and nitrogen in the polar upper atmosphere; called aurora borealis in the north and australis in the south.

Auroral oval Kutup ışığı ovali

The ring-shaped zone around each magnetic pole where auroras are most common; during geomagnetic storms it widens and shifts to lower latitudes.

Autoguiding Otomatik kılavuzlama

Using a separate small camera to watch a guide star and send continuous small corrections to the mount. It keeps stars pin-sharp during long exposures.

Automatic Dependent Surveillance–Broadcast (ADS-B) ADS-B

A surveillance technology in which an aircraft regularly broadcasts its satellite-derived position, speed and identity, which ground stations and other aircraft can receive.

Autonomous spaceport drone ship (ASDS) Otonom insansız iniş gemisi

SpaceX's uncrewed, self-positioning ocean platform on which rocket stages land. It is used when a stage lacks the propellant to return to the launch site.

Autopilot Otomatik pilot

An automatic flight control system that holds the heading, altitude and speed selected by the pilot; some systems can also perform automatic landings.

Autorotation Otorotasyon

A state in which, after engine failure, the rotor keeps turning from air flowing up through it as the helicopter descends, allowing a controlled emergency landing.

Auxiliary power unit (APU) Yardımcı güç ünitesi

A small gas turbine, usually in the tail, that supplies electrical power and conditioned air on the ground while the main engines are off, and helps start them.

Averted vision Kaçamak bakış

Spotting a faint object by looking slightly to one side of it. This places its light on the part of the retina richest in rod cells, which are more sensitive to dim light.

Avionics Aviyonik

The electronic systems used on aircraft and spacecraft, covering communication, navigation, flight management, displays and sensors.

Axes of flight Uçuş eksenleri

The three axes through an aircraft's centre of gravity: roll (longitudinal), pitch (lateral) and yaw (vertical); all of its rotations are described around them.

Axial precession (precession of the equinoxes) Presesyon (devinme)

The slow conical wobble of Earth's rotation axis, completing a cycle in about 25,800 years under the gravitational pull of the Sun and Moon, which makes the equinox points drift along the ecliptic.

Axial tilt (obliquity) Eksen eğikliği

The angle between a planet's rotation axis and the perpendicular to its orbital plane; for Earth it is about 23.44° and is the main cause of the seasons.

Axion Aksiyon

An extremely light hypothetical particle first proposed to solve a problem in particle physics. It is considered a leading dark matter candidate.

Azimuth Azimut

The direction angle of an object measured along the horizon, usually from north towards east, so that east is 90°, south 180° and west 270°.

Baikonur Cosmodrome Baykonur Kozmodromu

One of the world's first and largest spaceports, in Kazakhstan and leased by Russia. Sputnik 1 (1957) and Yuri Gagarin's flight (1961) launched from here.

Barlow lens Barlow merceği

A diverging lens placed before the eyepiece that increases a telescope's effective focal length, and thus its magnification, typically by two or three times.

Barred spiral galaxy Çubuklu sarmal galaksi

A spiral galaxy with a bar-shaped band of stars across its centre, with the arms emerging from the ends of the bar. Roughly two thirds of spirals are barred.

Barycenter (center of mass) Kütle merkezi (barimerkez)

The common centre of mass about which mutually orbiting bodies revolve; the Earth–Moon barycentre lies inside Earth, about 4,700 km from its centre.

Baryon acoustic oscillations (BAO) Baryon akustik salınımları

A characteristic scale of about 490 million light-years imprinted on the galaxy distribution by sound waves in the early universe. It serves as a standard ruler for the expansion history.

Baryon asymmetry Madde–antimadde asimetrisi

The puzzle that the universe contains far more matter than antimatter. Since the Big Bang should have made equal amounts, the cause of the imbalance remains unexplained.

Baryonic matter Baryonik madde

Ordinary matter made of protons and neutrons, forming stars, planets, gas and living things. It is only about 5% of the universe's total energy content.

BeiDou BeiDou

China's satellite navigation system. Besides MEO satellites it uses geostationary and inclined geosynchronous ones, and it began global service in 2020.

Bennu Bennu

A carbon-rich near-Earth asteroid roughly 500 m across. NASA's OSIRIS-REx collected material from its surface and returned it to Earth in September 2023.

Bernoulli's principle Bernoulli ilkesi

The principle that, in frictionless flow, static pressure falls as flow speed rises; it helps explain the lower pressure over a wing and underlies pitot airspeed measurement.

Berthing Yanaşma

Attachment in which a vehicle that has stopped close by is grappled by a robotic arm and placed onto a station port; cargo craft such as Cygnus arrive this way.

Betelgeuse Betelgeuse

A red supergiant marking Orion's shoulder and one of the brightest stars in the sky. Its Great Dimming of 2019–2020 made headlines, and it is expected to explode as a supernova eventually.

Big Bang Büyük Patlama

The cosmological model in which the universe expanded from an extremely hot, dense state about 13.8 billion years ago. It describes space expanding everywhere, not an explosion at one point.

Big Bang nucleosynthesis Büyük Patlama çekirdek sentezi

The formation of hydrogen, helium and traces of lithium nuclei in the universe's first few minutes. It explains the primordial mix of roughly 75% hydrogen and 25% helium by mass.

Big Crunch Büyük Çöküş

A hypothetical end in which expansion halts and reverses, collapsing everything back into a hot, dense state. The accelerating expansion makes it look unlikely.

Big Freeze (heat death) Büyük Donma

A possible end in which the universe expands and cools forever, stars burn out and no usable energy remains. It is the scenario most consistent with current observations.

Big Rip Büyük Yırtılma

A hypothetical fate in which growing dark energy eventually tears apart all structures, from galaxies down to atoms.

Binary black hole merger Kara delik birleşmesi

The inspiral and coalescence of two orbiting black holes into one as they lose energy. Such mergers are among the strongest sources of gravitational waves.

Binary pulsar (Hulse–Taylor pulsar) Çift pulsar (Hulse–Taylor pulsarı)

A pulsar in a binary with another neutron star; the first, PSR B1913+16, was found in 1974. The shrinking of its orbit through gravitational-wave emission earned the 1993 Nobel Prize in Physics.

Binary star Çift yıldız

A system of two stars orbiting their common center of mass. A large share of stars are in binary or multiple systems, and their orbits let astronomers measure stellar masses.

Binoculars Dürbün

A portable instrument with a separate optical system for each eye and prisms to correct the image. In a rating like 7x50, the numbers give magnification and objective diameter in millimetres.

Bioregenerative life support Biyorejeneratif yaşam desteği

An approach to life support for long missions in which plants and microorganisms renew air, water and food in a closed loop.

Biosignature Biyoişaret (biyoimza)

A substance, pattern or phenomenon that could indicate past or present life, such as oxygen and methane coexisting in a planet's atmosphere.

Bipropellant Çift bileşenli itken

A propellant system in which fuel and oxidizer are stored separately and combined in the combustion chamber. Nearly all large rocket engines are of this type.

Black dwarf Kara cüce

The hypothetical final state of a white dwarf that has cooled until it no longer shines. Because cooling takes far longer than the current age of the universe, none exist yet.

Black hole Kara delik

A region of spacetime whose gravity is so strong that nothing, not even light, can escape from inside its event horizon. They form from collapsing massive stars or at the centers of galaxies.

Blazar Blazar

An active galactic nucleus whose jet points almost straight at Earth. Relativistic effects boost its brightness, which can vary within hours; blazars are strong gamma-ray sources.

Blue straggler Mavi başıboş yıldız

A star in a cluster that is hotter and brighter than the turnoff stars and looks younger than it should. It is thought to form through stellar mergers or mass transfer in a binary.

Blue supergiant Mavi süperdev

An extremely luminous, hot and massive supergiant with a surface temperature of tens of thousands of kelvin. Rigel in Orion is the best-known example.

Blueshift Maviye kayma

The shortening of light's wavelength towards the blue end of the spectrum when its source approaches the observer. Light from the Andromeda Galaxy, for instance, is blueshifted.

Boeing Starliner (CST-100) Starliner

A crewed capsule built by Boeing for NASA's Commercial Crew Program, designed to land on the ground cushioned by airbags; its first crewed test flight launched in June 2024.

Bok globule Bok globülü

A small, dense, cold cloud of dust and gas that appears as a dark blot against a bright background. Stars can form inside them; they are named after Bart Bok.

Bolometer Bolometre

A detector that measures radiant power from the tiny temperature rise caused by absorbed radiation. It is widely used in submillimetre and infrared astronomy.

Bone density loss Kemik yoğunluğu kaybı

The loss of bone mineral when bones no longer bear loads in microgravity; without countermeasures, weight-bearing bones can lose about 1–1.5 percent of their density per month.

Book of Fixed Stars Sabit Yıldızlar Kitabı

A work written around 964 by ʿAbd al-Rahman al-Sufi describing the constellations and star brightnesses; it contains the earliest known record of the Andromeda galaxy, as a "little cloud".

Boostback burn Geri dönüş ateşlemesi

A manoeuvre after separation in which the first stage flips around and fires its engines to head back toward the launch site or landing zone.

Booster catch Kuleyle yakalama

Catching a returning booster in mid-air with movable arms on the launch tower instead of landing on legs. SpaceX first did it with Super Heavy in October 2024.

Bortle scale Bortle ölçeği

A nine-level scale rating night-sky darkness from 1, a pristine dark sky, to 9, an inner-city sky. John Bortle published it in 2001.

Boundary layer Sınır tabaka

The thin layer of air next to a surface in which viscosity slows the flow from free-stream speed down to zero at the wall; its separation can lead to a stall.

Brown dwarf Kahverengi cüce

An object of about 13 to 80 Jupiter masses, too light to sustain hydrogen fusion in its core. It sits between planets and stars and slowly cools and fades.

Bullet Cluster Mermi Kümesi

A system formed by two colliding galaxy clusters in which the hot gas and the centres of mass have separated. It is regarded as strong evidence for dark matter.

Bypass ratio Baypas oranı

In a turbofan, the mass of air bypassing the core divided by the mass flowing through it; it can exceed 10:1 on modern airliner engines, and higher ratios save fuel.

C

C band C bandı

The microwave band of roughly 4–8 GHz. Resistant to rain, it has long served satellite TV and data distribution in tropical regions, though it needs large dishes.

C-type asteroid C tipi asteroit

A class of very dark, carbon-rich asteroids that make up the majority of known asteroids. They are thought to preserve little-altered material from the early Solar System.

Cabin pressure Kabin basıncı

The air pressure inside a spacecraft; the ISS is kept at about 101 kPa, equal to sea level, with a nitrogen–oxygen mix similar to Earth's air.

Cabin pressurization Kabin basınçlandırması

Pumping compressed air into the cabin at high altitude so that interior pressure stays at a comfortable level, typically equivalent to 1,800–2,400 m.

Canadarm2 Canadarm2

The Canadian-built robotic arm of the ISS, about 17.6 m long, which captures arriving cargo craft and helps with assembly work and spacewalks.

Cape Canaveral Space Force Station Cape Canaveral Uzay Kuvvetleri İstasyonu

A US Space Force launch base right next to Kennedy Space Center. Rockets such as Falcon 9, Atlas V and Vulcan launch from its pads.

Capsule Kapsül

A wingless crewed spacecraft, usually with a blunt conical shape, that protects its crew through launch, flight and re-entry; Soyuz, Orion and Crew Dragon are examples.

Capsule communicator (CAPCOM) Kapsül haberleşmecisi

The person in mission control who speaks directly with the crew in space; traditionally the job is done by a fellow astronaut.

Carbon dioxide removal Karbondioksit giderimi

Capturing the carbon dioxide that the crew breathe out using absorbent materials, then venting or recycling it; high CO₂ levels cause headaches and impaired thinking.

Carbonaceous chondrite Karbonlu kondrit

A rare type of chondrite rich in carbon, water-bearing minerals and organic molecules such as amino acids. The Murchison and Allende meteorites are famous examples.

Career radiation exposure limit Kariyer radyasyon dozu sınırı

The maximum radiation dose an astronaut may receive over an entire career; since 2022 NASA has applied a single 600-millisievert limit to everyone.

Cargo spacecraft Kargo uzay aracı

An uncrewed resupply vehicle that delivers food, water, propellant, experiments and spare parts to a space station; Progress, Cygnus and Cargo Dragon are examples.

Carrington Event Carrington Olayı

The most intense geomagnetic storm on record, in early September 1859; it disrupted telegraph lines and produced auroras visible even in the tropics.

Cassegrain telescope Cassegrain teleskobu

A reflector design in which a convex secondary mirror sends light back through a central hole in the concave primary mirror, bringing it to focus behind it.

Cassini Division Cassini aralığı

A dark gap about 4,800 km wide between Saturn's A and B rings, spotted by Giovanni Domenico Cassini in 1675. It is not empty but contains sparse particles.

Cataclysmic variable Kataklizmik değişen

A binary in which a white dwarf draws material from a close companion and undergoes sudden outbursts. Novae and dwarf novae belong to this class.

Catadioptric telescope Katadioptrik teleskop

A telescope that forms images using both mirrors and lenses. Because the light path is folded, a long focal length fits into a short, portable tube.

Celestial equator Gök ekvatoru

The great circle where the plane of Earth's equator meets the celestial sphere; it divides the sky into northern and southern halves and marks zero declination.

Celestial mechanics Gök mekaniği

The branch of astronomy that studies the motions of celestial bodies under gravity, using Newton's and Kepler's laws to calculate the positions of planets and moons.

Celestial pole Gök kutbu

Either of the two points where Earth's rotation axis, extended into space, meets the celestial sphere; the north celestial pole currently lies very close to Polaris.

Celestial sphere Gök küresi

An imaginary sphere of infinite radius centred on the observer, onto which celestial objects are projected; it lets sky positions be described purely by angles.

Centaur Kentaur

An icy small body orbiting between Jupiter and Neptune and crossing the giant planets' orbits, sometimes showing both asteroid and comet traits. The first known was 2060 Chiron.

Center of gravity (CG) Ağırlık merkezi

The point through which an aircraft's total weight is considered to act; loading and fuel are planned so that it stays within certified limits for safe flight.

Cepheid variable Sefeid değişeni

A luminous yellow supergiant that pulsates with a regular period of 1 to 100 days. Because its period is tied to its luminosity, it is used to measure distances to galaxies.

Ceres Ceres

The largest object in the asteroid belt between Mars and Jupiter and the only dwarf planet there. Giuseppe Piazzi discovered it in 1801; the Dawn spacecraft orbited it from 2015.

Challenger disaster Challenger faciası

The break-up of the shuttle Challenger 73 seconds after launch on 28 January 1986, caused by a failed seal in a solid rocket booster; all seven astronauts died.

Chandrasekhar limit Chandrasekhar limiti

The maximum mass a white dwarf can support by electron degeneracy pressure, about 1.4 solar masses. A white dwarf pushed past this limit collapses or explodes.

Charge-coupled device (CCD) Yük bağlantılı aygıt (CCD)

A light-sensing chip that converts photons into electric charge and reads it out by shifting it across the pixels. Invented in 1969, it won a 2009 Nobel and replaced photographic plates in astronomy.

Charon Charon (Kharon)

Pluto's largest moon, slightly more than half Pluto's diameter. Because their shared centre of mass lies outside Pluto, the pair is often described as a binary dwarf planet.

Chelyabinsk event Çelyabinsk olayı

The airburst of an asteroid about 20 m across over Russia on 15 February 2013. Its shock wave shattered windows and injured around 1,500 people.

Chelyabinsk meteor Çelyabinsk meteoru

The airburst of a roughly 20-metre asteroid over Russia on 15 February 2013, whose shock wave shattered windows and injured about 1,500 people.

Chicxulub crater Chicxulub krateri

A buried impact crater about 180 km wide on Mexico's Yucatán Peninsula. It is linked to the mass extinction that wiped out the non-avian dinosaurs about 66 million years ago.

Chondrite Kondrit

A stony meteorite containing chondrules, millimetre-sized spherical mineral grains. Chondrites make up most meteorite falls and preserve some of the Solar System's oldest solid material.

Chromatic aberration Renk sapması (kromatik aberasyon)

Coloured fringes around bright objects caused by a lens focusing different wavelengths at different points. Mirrors do not suffer from it, and special lens designs reduce it.

Chromosphere Kromosfer

The thin atmospheric layer just above the photosphere, glimpsed as a reddish rim during total solar eclipses and named for that colour.

Circadian rhythm Sirkadiyen ritim

The body's roughly 24-hour biological clock; since the ISS sees about 16 sunrises a day, astronauts' sleep is managed with lighting and schedules.

Circumpolar star Çevrekutupsal yıldız

A star close enough to the celestial pole, for a given latitude, that it never sets and stays above the horizon all night; from Istanbul every star of the Little Dipper behaves this way.

CMB anisotropies KMA anizotropileri

Temperature variations of about one part in 100,000 in the cosmic microwave background. They trace density ripples in the early universe and let cosmological parameters be measured.

CMOS sensor CMOS algılayıcı

A semiconductor image sensor in which each pixel has its own amplifier, allowing fast readout and low power use. Most amateur astronomy cameras now use it.

CNO cycle CNO döngüsü

A fusion cycle that converts hydrogen into helium with carbon, nitrogen and oxygen nuclei acting as catalysts. It dominates in stars more than about 1.3 times the Sun's mass.

Cockpit (flight deck) Kokpit (pilot kabini)

The compartment from which pilots fly the aircraft, containing the flight instruments, controls and communication equipment.

Cold dark matter (CDM) Soğuk karanlık madde

Dark matter assumed to consist of particles moving slowly compared with light in the early universe. It predicts that structures formed hierarchically, from small to large.

Cold gas thruster Soğuk gaz iticisi

A simple thruster that releases pressurized gas such as nitrogen through a small nozzle without combustion. Its specific impulse is low; it is used for fine attitude control and small satellites.

Collective pitch control Kolektif kumanda

The lever that changes the pitch of all main rotor blades together, controlling total lift and therefore climb and descent.

Collimation Kolimasyon

The process of aligning a telescope's mirrors and lenses precisely along the optical axis. A poorly collimated telescope gives soft, distorted star images.

Collision avoidance maneuver Çarpışmadan kaçınma manevrası

A burn of a satellite's or station's thrusters to change its orbit and move away from an object whose collision probability exceeds a set threshold.

Color index Renk ölçeği (renk indisi)

The difference between a star's magnitudes measured in two filters, such as B−V. It indicates temperature: small for hot blue stars and large for cool red ones.

Columbia disaster Columbia faciası

The loss of the shuttle Columbia during re-entry on 1 February 2003, after foam shed at launch had punched a hole in its wing; seven astronauts died.

Coma Koma

The hazy envelope of gas and dust that forms around a comet's nucleus as it warms near the Sun. It can grow to hundreds of thousands of kilometres across.

Coma (optical aberration) Koma (optik sapma)

An aberration that makes stars near the edge of the field look like little comets stretched in one direction. It is most noticeable in fast parabolic mirrors.

Combustion chamber Yanma odası

The part of the engine where fuel and oxidizer mix and burn at high pressure and temperature. The hot gas produced there flows into the nozzle to be accelerated.

Combustion instability Yanma kararsızlığı

Pressure oscillations in the combustion chamber that feed on acoustic vibration and grow until they can destroy the engine. It was one of the hardest problems in developing the F-1.

Comet Kuyruklu yıldız

A small body with a nucleus of ice, dust and rock. As it nears the Sun its ices vaporise, producing a glowing coma and long tails.

Comet nucleus Kuyruklu yıldız çekirdeği

The solid core of a comet, typically a few kilometres across and made of ice and dust beneath a very dark crust. It is often likened to a 'dirty snowball'.

Comet Shoemaker–Levy 9 Shoemaker–Levy 9

A comet torn apart by Jupiter's gravity whose fragments slammed into Jupiter in July 1994. It was the first collision between two Solar System bodies to be observed directly.

Commercial Crew Program Ticari Mürettebat Programı

A NASA programme that buys astronaut transport to the International Space Station from private companies; Crew Dragon and Starliner were developed under it.

Commercial space station Ticari uzay istasyonu

A space station built and run by private companies rather than a government agency, leased out for research, manufacturing or tourism; such stations are expected to succeed the ISS.

Committee on the Peaceful Uses of Outer Space (COPUOS) BM Uzayın Barışçıl Kullanımı Komitesi (COPUOS)

The UN committee, established in 1959, that fosters international cooperation on the peaceful use of space and drafted the core space treaties.

Compact object Sıkı cisim (kompakt cisim)

The collective name for the ultra-dense remnants left by dead stars: white dwarfs, neutron stars and black holes. Degeneracy pressure or gravity, rather than ordinary gas pressure, governs them.

Composite material Kompozit malzeme

A light, strong material made by embedding fibres such as carbon or glass in resin; it makes up roughly half the structure of the Boeing 787 and Airbus A350.

Concorde Concorde

An Anglo-French supersonic airliner that cruised at about Mach 2, crossing the Atlantic in around three and a half hours between 1976 and 2003.

Conjunction Kavuşum

The occasion when two celestial bodies share the same longitude, or appear very close together, as seen from Earth; for a planet it usually means lining up with the Sun.

Conservation of angular momentum Açısal momentumun korunumu

The principle that a system's total angular momentum stays constant when no external torque acts; it explains why planets move faster near perihelion.

Constellation Takımyıldız

Each of the officially bounded regions into which the sky is divided; the International Astronomical Union recognises 88 constellations covering the whole celestial sphere.

Continuous spectrum Sürekli tayf

A spectrum that runs unbroken across a wide range of wavelengths, without lines. It is produced by hot, dense bodies such as a glowing filament or a star's interior layers.

Control tower Kule (meydan kontrolü)

The air traffic control unit at an airport that visually manages take-offs, landings and ground movements on and around the runways.

Coordinated Universal Time (UTC) Eşgüdümlü Evrensel Zaman (UTC)

The international time standard based on atomic clocks and kept in step with Earth's rotation by occasional leap seconds; Turkey's time zone is UTC+3.

Core-collapse supernova Çekirdek çökmeli süpernova

A supernova produced when the iron core of a star above about 8 solar masses collapses and its outer layers are blasted away. It leaves behind a neutron star or a black hole.

Corona Korona (taç)

The Sun's outermost atmosphere, hotter than a million degrees, which becomes visible only during total eclipses or with a coronagraph.

Coronagraph Koronagraf

An instrument that blocks the light of a bright source to reveal faint features around it. First developed for the solar corona, it is now used to image exoplanets directly.

Coronal hole Koronal delik

A region where magnetic field lines open into space, appearing dark in ultraviolet and X-ray images; it is the main source of the fast solar wind.

Coronal mass ejection (CME) Koronal kütle atımı (KKA)

The eruption of billions of tonnes of magnetized plasma from the solar corona; Earth-directed ones typically arrive within 1–3 days and can trigger geomagnetic storms.

Cosmic dark ages Karanlık çağlar

The period of a few hundred million years between recombination and the birth of the first stars and galaxies, when the universe had no sources of light.

Cosmic dawn Kozmik şafak

The era, roughly 100–200 million years after the Big Bang, when the first stars and galaxies began to shine. The James Webb Space Telescope is probing this epoch.

Cosmic distance ladder Kozmik uzaklık merdiveni

The chain of methods, such as parallax, Cepheid variables and Type Ia supernovae, each calibrating the next to measure ever greater distances.

Cosmic inflation Kozmik enflasyon

The theory that the universe expanded exponentially during a tiny fraction of its first second. It accounts for the universe's flatness, uniformity and the fluctuations that seeded structure.

Cosmic microwave background (CMB) Kozmik mikrodalga artalan ışınımı

Radiation released about 380,000 years after the Big Bang that now arrives from every direction as microwaves at 2.725 K. It is the most important evidence about the early universe.

Cosmic ray Kozmik ışın

High-energy particles, mostly protons and atomic nuclei, that arrive from space and strike the atmosphere. Their sources include supernova remnants and active galaxies.

Cosmic void Kozmik boşluk

A vast region between the filaments of the cosmic web containing very few galaxies. Voids can be tens to hundreds of millions of light-years across; the Boötes Void is a known example.

Cosmic web Kozmik ağ

The large-scale pattern in which galaxies lie along filaments, walls and nodes surrounding enormous voids. It is shaped by the gravity of dark matter.

Cosmological constant (Λ) Kozmolojik sabit

A term Einstein added to his field equations, representing a constant energy density of empty space. Today it is the simplest explanation for dark energy.

Cosmological principle Kozmolojik ilke

The assumption that on large enough scales the universe is homogeneous (the same everywhere) and isotropic (the same in every direction). It underpins modern cosmology.

Cosmological redshift Kozmolojik kırmızıya kayma

The stretching of light's wavelength from distant sources as space expands during its journey. The redshift value z indicates a galaxy's distance and the epoch the light left it.

Cosmology Kozmoloji

The science of the origin, structure, evolution and fate of the universe as a whole. It combines observational astronomy with theoretical physics.

Cosmonaut Kozmonot

The title given to space travellers of the Soviet and Russian space programmes; the first, Yuri Gagarin, completed one orbit of Earth in 1961.

Countdown Geri sayım

The timeline of pre-launch operations counted down as T-minus, with liftoff at zero. It can be paused by planned or unplanned holds.

Crab Nebula (M1) Yengeç Bulutsusu (M1)

The remnant in Taurus of a supernova recorded by Chinese astronomers in 1054. At its center is a pulsar spinning about 30 times per second.

Crew Mürettebat

All the astronauts assigned to a spacecraft or station, filling roles such as commander, pilot and specialists.

Crew Dragon Crew Dragon

A SpaceX-built capsule that ferries astronauts to low Earth orbit; it made its first crewed flight in May 2020 and splashes down in the ocean under parachutes.

Crewed mission to Mars Mars'a insanlı görev

The concept of sending people to Mars and bringing them home; each leg takes six to nine months and the whole mission could last two to three years.

Critical density Kritik yoğunluk

The average density needed for the universe to be spatially flat, today equivalent to about five or six hydrogen atoms per cubic metre.

Crosswind landing Yan rüzgârlı iniş

A landing in wind blowing across the runway; the pilot counters drift by pointing the nose into the wind or lowering the upwind wing.

Cryogenic propellant Kriyojenik itken

A propellant that stays liquid only at very low temperatures. Liquid oxygen boils near −183 °C and liquid hydrogen near −253 °C, so both need insulated tanks.

Cryovolcanism Kriyovolkanizma (buz volkanizması)

Volcanic activity that erupts volatiles such as water, ammonia or methane as liquid or vapour instead of molten rock. It has been observed on Enceladus and Triton.

CubeSat CubeSat (küp uydu)

A standard small-satellite format built from 10 cm cube units (1U). Produced in sizes such as 1U, 3U and 6U, they ride to orbit cheaply alongside other payloads.

Culmination (meridian transit) Kulminasyon (meridyenden geçiş)

The moment an object crosses the celestial meridian during its daily motion; at upper culmination it reaches its greatest altitude above the horizon.

Cumulonimbus (Cb) Kümülonimbüs

A towering cloud that can extend more than 10 km vertically, producing thunderstorms, severe turbulence, hail and icing; aircraft avoid it by a wide margin.

Cupola Cupola

A seven-window observation module added to the ISS in 2010, from which the crew watch Earth and oversee robotic-arm operations.

Cyclic pitch control Siklik kumanda

The control stick that varies blade pitch cyclically through each revolution, tilting the rotor disc to move the helicopter forwards, backwards or sideways.

Cygnus X-1 Kuğu X-1 (Cygnus X-1)

A strong X-ray source in Cygnus discovered in 1964. It pairs a blue supergiant with a black hole of about 21 solar masses and was the first widely accepted black hole.

Dark adaptation Karanlığa uyum

The eye's gradual increase in sensitivity in the dark. Full adaptation takes about 20 to 30 minutes, and observers use red lights because white light spoils it.

Dark current Karanlık akım

Charge that builds up in pixels from heat even when no light falls on the sensor. Because it rises steeply with temperature, astronomy cameras are cooled.

Dark energy Karanlık enerji

The unknown component thought to drive the accelerating expansion of the universe, accounting for about 68% of its total energy content.

Dark frame Karanlık kare

An exposure taken with the telescope covered, matching the light frame's duration and temperature. It is used to subtract dark current and hot pixels from the image.

Dark matter Karanlık madde

Matter that neither emits nor reflects light and is detected only through its gravity. It is thought to make up about 85% of all matter, though its nature is still unknown.

Dark matter halo Karanlık madde halesi

The extended region of dark matter enveloping a galaxy or cluster, much larger and more massive than the visible matter. Galaxies form at the centres of these haloes.

Dark nebula Karanlık bulutsu

A dense cloud of dust that blocks light from stars or bright nebulae behind it. The Horsehead Nebula is the best-known example.

Dawes' limit Dawes sınırı

An empirical limit for visually splitting two equally bright stars. In arcseconds it is about 116 divided by the aperture in millimetres.

de Laval nozzle De Laval lülesi

A nozzle that first narrows and then widens: gas reaches the speed of sound at the throat and goes supersonic in the diverging section. Almost every rocket engine uses this principle.

Declination (Dec) Dik açıklık (deklinasyon)

The angular distance of an object north or south of the celestial equator, ranging from +90° to −90°; it is the sky's equivalent of geographic latitude.

Decompression sickness Dekompresyon hastalığı

Joint pain and nervous-system problems caused when nitrogen dissolved in the blood forms bubbles after a rapid drop in surrounding pressure; divers call it the bends.

Deep Space Network (DSN) Derin Uzay Ağı

NASA's network of giant antennas near Goldstone (USA), Madrid (Spain) and Canberra (Australia) for talking to interplanetary spacecraft. Spaced about 120° apart, they give continuous coverage.

Deep-sky object (DSO) Derin gök cismi

A general term for faint objects beyond the Solar System that are not individual stars, such as nebulae, star clusters and galaxies.

Delta wing Delta kanat

A triangular, highly swept wing offering low drag and a strong structure at supersonic speeds, used on Concorde and many fighter aircraft.

Delta-v (Δv) Delta-v (hız değişimi)

The change in velocity a spacecraft must produce to change orbit or perform a manoeuvre; in mission planning it is the key measure of propellant needs.

Density parameter (Omega, Ω) Yoğunluk parametresi (Ω)

The ratio of the universe's actual average density to the critical density. Ω = 1 corresponds to flat geometry, Ω > 1 to closed and Ω < 1 to open.

Density wave theory Yoğunluk dalgası kuramı

The theory that spiral arms are compression waves travelling through the disk rather than fixed groups of stars. Gas passing through them is squeezed, triggering star formation.

Deorbiting Yörüngeden çıkarma

Lowering a satellite's orbit at the end of its mission so that it burns up in the atmosphere or falls into a safe ocean area.

Design life Tasarım ömrü

The period a spacecraft is built to operate. For geostationary communication satellites it is typically 15 years; many probes, such as Voyager, have exceeded theirs many times over.

Differential photometry Diferansiyel fotometri

Measuring a target's brightness relative to comparison stars in the same image. Because atmospheric changes affect both alike, it gives very precise results.

Diffraction grating Kırınım ağı

An optical surface ruled with many closely spaced parallel lines that splits light into its wavelengths by interference. It has replaced the prism in most modern spectrographs.

Diffraction limit Kırınım sınırı

The best resolution a telescope can theoretically reach, set by the wave nature of light. It is roughly 1.22 times the wavelength divided by the aperture, in radians.

Dimorphos Dimorphos

A roughly 160-metre moonlet orbiting the asteroid Didymos. NASA's DART probe struck it in 2022, shortening its orbit by about 32 minutes in the first planetary defence test.

Direct imaging Doğrudan görüntüleme

Photographing an exoplanet's own light after blocking the star's glare with tools such as coronagraphs; it works best for young, massive planets far from their stars.

Direct-to-device (D2D) Doğrudan cihaza bağlantı

Satellites communicating directly with ordinary mobile phones without special terminals, offering messaging and limited data where there is no terrestrial network.

Distance modulus Uzaklık modülü

The difference between an object's apparent and absolute magnitudes, m − M = 5 log₁₀(d/10 pc), which gives its distance directly.

Dobsonian telescope Dobson teleskobu

A Newtonian reflector on a simple, low altazimuth base. Popularised by John Dobson, it offers large aperture at low cost and is much loved by amateur observers.

Docking Kenetlenme

The joining of a spacecraft to its target under its own power through a docking mechanism; Soyuz and Crew Dragon attach to the ISS this way.

Double Asteroid Redirection Test (DART) DART görevi

The first planetary-defense test, in which a NASA spacecraft struck the asteroid moonlet Dimorphos on 26 September 2022, shortening its orbit by about 32 minutes.

Downlink Aşağı bağlantı

The radio link from a satellite or spacecraft down to the ground, carrying telemetry, imagery and broadcast signals.

Drag Sürükleme kuvveti

The resistive force acting on a body moving through air, opposite to its direction of motion; it grows with the square of speed and must be overcome by engine thrust.

Drake equation Drake denklemi

A formula proposed by Frank Drake in 1961 that estimates the number of communicating civilizations in our galaxy from factors such as star-formation rate and the odds of life arising.

Dust tail Toz kuyruğu

A curved, yellowish-white tail of dust particles pushed away from a comet by the pressure of sunlight. It shines by reflected sunlight.

Dwarf galaxy Cüce galaksi

A small galaxy containing a few billion stars or fewer. Many orbit larger galaxies such as the Milky Way as satellites.

Dwarf planet Cüce gezegen

A body that orbits the Sun and is nearly round but has not cleared its orbital neighbourhood and is not a moon. Pluto, Ceres and Eris are examples.

Earth Dünya

The third planet from the Sun and the only known world with stable liquid water on its surface and life. Its single natural satellite is the Moon.

Earth observation satellite Yer gözlem uydusu

A satellite designed to image or measure Earth's land, oceans and atmosphere. Examples include Landsat, the Sentinel series and Türkiye's İMECE.

Earth's rotation boost Dünya'nın dönüşünden kazanç

The extra speed rockets gain by launching eastward with Earth's spin. At the equator it is about 465 m/s, which is why spaceports are placed as close to the equator as possible.

Eccentricity Dış merkezlik (basıklık)

A number describing how far an orbit departs from a circle: 0 for a circle, between 0 and 1 for an ellipse, exactly 1 for a parabola and greater than 1 for a hyperbola.

Eclipse Tutulma

The darkening of one body as it passes into another's shadow or behind it; in a solar eclipse the Moon covers the Sun, while in a lunar eclipse the Moon enters Earth's shadow.

Eclipse season Tutulma mevsimi

The periods around the equinoxes when geostationary satellites pass through Earth's shadow once a day. Each eclipse lasts at most about 72 minutes, during which the satellite runs on batteries.

Eclipsing binary Örten çift (tutulmalı çift)

A binary whose orbit is nearly edge-on to us, so the stars regularly eclipse each other. Its light curve reveals the stars' sizes; Algol is the most famous example.

Ecliptic Ekliptik (tutulum)

The apparent annual path of the Sun against the stars; it is the projection of Earth's orbital plane onto the sky and is tilted about 23.4° to the celestial equator.

Eddington limit Eddington limiti

The maximum luminosity at which radiation pressure exactly balances gravity. Above it a star or accretion disk begins blowing its outer layers into space.

Effective temperature Etkin sıcaklık

The temperature of a blackbody of the same radius that would emit the same total power as the star. It is the standard measure of stellar surface temperature, about 5,770 K for the Sun.

Einstein ring Einstein halkası

A ring-shaped image of a distant source formed when the source, lensing mass and observer are almost perfectly aligned. It is a case of strong gravitational lensing.

Electric propulsion Elektrikli itki

Propulsion that uses electrical power to ionize or heat a propellant and accelerate it. Thrust is tiny, but specific impulse is many times that of chemical rockets.

Electric-pump-fed engine Elektrikli pompa beslemeli motor

An engine whose propellant pumps are driven by battery-powered electric motors instead of a turbine. Rocket Lab's Rutherford, used on Electron, was the first orbital engine to work this way.

Electrical power subsystem (EPS) Elektrik güç alt sistemi

The subsystem that generates, stores, regulates and distributes electricity on a spacecraft, typically made up of solar arrays, batteries and power-conditioning units.

Electromagnetic spectrum Elektromanyetik tayf

The full range of electromagnetic radiation ordered by wavelength, from radio waves through microwaves, infrared, visible light and ultraviolet to X-rays and gamma rays.

Electron degeneracy pressure Elektron yozlaşma basıncı

Pressure arising because the Pauli exclusion principle forbids electrons from being squeezed into the same quantum state. It does not depend on temperature and holds white dwarfs up against collapse.

Elevation angle Yükseliş açısı

The angle between the line of sight to a satellite and the local horizon. At low angles the signal travels farther through the atmosphere and may be blocked by obstacles.

Elevator İrtifa dümeni

A control surface hinged to the rear of the horizontal stabiliser that raises or lowers the nose to control pitch.

Elliptical galaxy Eliptik galaksi

A galaxy with no obvious disk or spiral arms, ranging from nearly spherical to flattened ellipsoids. It is dominated by old stars and holds little cold gas.

Elongation Uzanım (elongasyon)

The angular distance between a planet or other body and the Sun as seen from Earth; Mercury and Venus are best placed for viewing near greatest elongation.

Emission line Salma çizgisi (yayınım çizgisi)

A bright line in a spectrum produced when hot, thin gas emits light at particular wavelengths. Nebula spectra are dominated by such lines.

Emission nebula Salma bulutsusu

A cloud of gas ionized by ultraviolet light from nearby hot stars, so that it glows with its own light. Hydrogen emission usually makes it look red in photographs.

Empennage Kuyruk takımı (empenaj)

The tail assembly at the rear of an aircraft, made up of the horizontal and vertical stabilisers with the elevator and rudder; it provides stability and control.

Enceladus Enceladus

An icy moon of Saturn about 500 km across. Jets of water vapour and ice erupting from cracks near its south pole reveal a subsurface ocean and feed Saturn's E ring.

Engine clustering Motor kümelenmesi

Using several engines together on one stage instead of a single large one. Falcon 9's first stage has 9 engines and the Super Heavy booster has 33.

Entry, descent and landing (EDL) Giriş, alçalma ve iniş

The phase from a vehicle's atmospheric entry to touchdown. At Mars it lasts about seven minutes and uses a heat shield, parachute and rockets in sequence.

Environmental Control and Life Support System (ECLSS) Çevre kontrol ve yaşam destek sistemi

The ISS hardware covering oxygen generation, carbon dioxide removal, water recovery, humidity and temperature control and fire detection.

Ephemeris Efemeris (gök cetveli)

A table or data file giving the computed positions and velocities of celestial bodies or spacecraft at given times; it is a basic resource for observing and mission planning.

Epoch of reionization Yeniden iyonlaşma çağı

The era when ultraviolet light from the first stars and galaxies ionized the intergalactic hydrogen again. It was largely complete about a billion years after the Big Bang.

Equation of time Zaman denklemi

The difference between apparent solar time, shown by a sundial, and mean solar time; over the year it varies between about −14 and +16 minutes.

Equatorial coordinate system Ekvatoral koordinat sistemi

A celestial coordinate system based on the celestial equator that gives positions as right ascension and declination; it is the standard for star catalogues and telescope pointing.

Equatorial mount Ekvatoryal kundak

A telescope mount with one axis aligned parallel to Earth's rotation axis. It follows the daily motion of celestial objects by turning around that single axis.

Equinox Ekinoks (gece-gündüz eşitliği)

The moment the Sun crosses the celestial equator, when day and night are roughly equal in length; it occurs around 20–21 March and 22–23 September each year.

Equivalence principle Eşdeğerlik ilkesi

The principle that the local effects of a gravitational field cannot be distinguished from those of an accelerating reference frame; it is a cornerstone of general relativity.

Equivalent isotropically radiated power (EIRP) Eşdeğer izotropik yayılım gücü

Transmitter power multiplied by antenna gain: the power an ideal antenna radiating equally in all directions would need to produce the same signal strength. Usually quoted in dBW.

Ergosphere Ergosfer

The region just outside a rotating black hole's event horizon where spacetime is dragged around with the hole. Nothing can stay still there, though escape is still possible.

Eris Eris

A dwarf planet found in 2005, close to Pluto in size but more massive. Its discovery prompted the redefinition of 'planet' and Pluto's reclassification as a dwarf planet.

Escape velocity (second cosmic velocity) Kaçış hızı (ikinci kozmik hız)

The minimum speed an unpowered object needs to break free of a body's gravity entirely; about 11.2 km/s at Earth's surface and 2.4 km/s on the Moon.

Eta Carinae Eta Carinae

A massive, unstable binary system in Carina about 7,500 light-years away. During its Great Eruption in the 1840s it briefly became one of the brightest stars in the sky.

Euclid (space telescope) Euclid Uzay Teleskobu

ESA's space telescope, launched in 2023, that measures the shapes and distances of billions of galaxies to study dark matter and dark energy.

Europa Europa

An ice-covered moon of Jupiter thought to hide a salty ocean beneath its crust, possibly holding more water than all of Earth's oceans. NASA launched Europa Clipper toward it in 2024.

Event horizon Olay ufku

The boundary around a black hole beyond which not even light can return. Events inside it can never be observed from outside.

Exercise countermeasures Önleyici egzersiz

The mandatory workouts, about two hours a day on treadmills, cycle ergometers and resistance machines, that astronauts do to limit muscle and bone loss in microgravity.

Exhaust velocity Egzoz hızı

The speed at which combustion products leave the nozzle. Effective exhaust velocity equals specific impulse multiplied by standard gravity and is the key parameter in the rocket equation.

Exit pupil Çıkış gözbebeği

The diameter of the beam of light leaving the eyepiece. It equals aperture divided by magnification; if it is larger than the eye's pupil, some light is wasted.

Exoplanet Ötegezegen (dış gezegen)

A planet orbiting a star other than the Sun, or drifting free of any star; by 2025 the confirmed tally had passed 6,000.

Expander cycle Genleştirici çevrim

A cycle in which fuel is heated and vaporized in the engine walls and then drives the turbine, with no preburner needed. It is common in hydrogen upper stages; the RL10 is a well-known example.

Expansion of the universe Evrenin genişlemesi

The increase over time in the distances between galaxies because space itself is stretching. It was established in the 1920s through the work of Lemaître and Hubble.

Expansion ratio Genleşme oranı

The ratio of nozzle exit area to throat area. Vacuum-optimized upper-stage engines use very large ratios, while sea-level engines use smaller ones to avoid flow separation.

Expedition Sefer

The name for a period of long-duration crew residence on the ISS; expeditions are numbered and typically last around six months.

Exposure time Pozlama süresi

The length of time a detector or film collects light. It can run to minutes for faint deep-sky objects or just milliseconds for bright planets.

Extended-range twin-engine operations (ETOPS) ETOPS

The special approval and rules allowing twin-engine airliners to fly routes more than 60 minutes from the nearest suitable airport; common on transoceanic flights.

Extensive air shower Hava sağanağı

The cascade of billions of secondary particles produced when a high-energy cosmic ray hits nuclei in the atmosphere. It is measured with ground-based detector arrays.

Extravehicular activity (EVA) Araç dışı faaliyet

The technical term for any work an astronaut does outside a spacecraft's pressurized cabin, whether in open space or on the surface of another body.

Extravehicular Mobility Unit (EMU) Araç Dışı Hareketlilik Birimi

NASA's spacesuit for shuttle and ISS spacewalks, made up of a hard upper torso and a backpack-style life support unit.

Extremely Large Telescope (ELT) Aşırı Büyük Teleskop (ELT)

An optical and infrared telescope being built in Chile by the European Southern Observatory, with a 39-metre segmented primary mirror. It will be the world's largest optical telescope.

Extremophile Ekstremofil

An organism, usually microbial, that thrives in conditions lethal to most life, such as extreme heat, pressure, acidity, salinity or radiation.

Eyepiece (ocular) Göz merceği (oküler)

The lens assembly that magnifies the image formed by a telescope for viewing by eye. Swapping eyepieces of different focal lengths changes the magnification.

F-1 engine F-1 motoru

The gas-generator engine, burning RP-1 and liquid oxygen, used in a cluster of five on Saturn V's first stage. It is the most powerful single-chamber liquid rocket engine ever flown.

Falcon 9 Falcon 9

SpaceX's two-stage medium-lift rocket burning RP-1 and liquid oxygen. Its first stage runs on nine Merlin engines and is recovered by propulsive landing for reuse.

False-color image Yanlış renkli görüntü

An image made by assigning visible colours to data from invisible wavelengths or narrow bands. Many of Hubble's famous nebula pictures were produced this way.

Far side of the Moon Ay'ın uzak yüzü

The lunar hemisphere never seen from Earth because of tidal locking. It is not dark and receives sunlight; China's Chang'e 4 made the first soft landing there in 2019.

Fast radio burst (FRB) Hızlı radyo patlaması

An intense radio flash lasting only milliseconds, usually from other galaxies. First found in 2007, some have been traced to magnetars.

Fermi paradox Fermi paradoksu

The contradiction between the expectation that the galaxy should hold many civilizations and the absence of any evidence for them, named after Enrico Fermi's question "Where is everybody?"

Field of view (FOV) Görüş alanı

The angular width of sky visible at once through a telescope, binocular or camera. It is usually expressed in degrees or arcminutes.

Finderscope Arayıcı dürbün

A small, wide-field telescope or sight attached to the main instrument. It helps locate a target and bring it into the main telescope's narrow field of view.

Fireball (bolide) Ateş topu (bolid)

A meteor brighter than about magnitude −4, outshining Venus. Some explode in the sky as they break apart; these are often called bolides.

Flame trench Alev kanalı

A trench lined with concrete and heat-resistant material that channels hot engine exhaust away from the pad at liftoff, protecting vehicle and pad from reflected flame and sound.

Flap Flap

A trailing-edge surface that extends downward to increase wing camber and often area, giving enough lift at lower speeds for take-off and landing.

Flat field Düz alan karesi (flat)

An image of an evenly illuminated surface. It is used to correct uneven response such as dust shadows, vignetting and pixel-to-pixel sensitivity differences.

Flatness problem Düzlük problemi

The question of why the universe's density is so finely tuned to the critical density that space is almost perfectly flat. Inflation was proposed partly to explain it.

Flexible Image Transport System (FITS) FITS biçimi

The standard digital file format in astronomy for storing images, spectra and tables along with descriptive headers. Defined in 1981, it is used by most observatories to publish data.

Flight control surfaces Kumanda yüzeyleri

Movable parts such as ailerons, elevator and rudder that alter the airflow over the wings and tail to steer the aircraft about its three axes.

Flight director Uçuş direktörü

The official in mission control in charge of a spaceflight in real time, with final say on decisions affecting crew safety.

Flight level (FL) Uçuş seviyesi

An altitude based on the standard pressure setting of 1013.25 hPa and expressed in hundreds of feet; FL350, for example, is a pressure altitude of 35,000 ft.

Flight management system (FMS) Uçuş yönetim sistemi

An onboard computer system that combines the flight plan, navigation data and performance calculations to manage the route and vertical profile automatically.

Flight plan Uçuş planı

A document filed with air traffic services before departure listing the route, altitude, speed, departure and destination airfields, estimated time and alternate.

Flight recorder (black box) Kara kutu

Crash-protected recorders comprising the flight data recorder and cockpit voice recorder; they are painted orange for easy recovery and carry an underwater locator beacon.

Flight simulator Uçuş simülatörü

A device that realistically reproduces an aircraft's cockpit and flight behaviour, letting pilots practise emergencies in training without risk.

Flight surgeon Uçuş cerrahı

An aerospace physician who monitors astronauts' health from training through to post-flight and gives medical support from the ground during missions.

Flight termination system (FTS) Uçuş sonlandırma sistemi

A safety system that destroys a rocket in flight or shuts down its engines if it strays off course and endangers people. Most rockets now carry an autonomous version.

Fluid shift Sıvı kayması

The movement of body fluids from the legs towards the head and chest in microgravity, giving astronauts puffy faces, stuffy noses and thinner legs.

Fly-by-wire Elektronik uçuş kontrolü (fly-by-wire)

A system in which pilot inputs are converted into electrical signals and passed via computers to the control surfaces instead of through mechanical linkages; it can provide flight-envelope protection.

Flyby Yakın geçiş

A mission type in which a spacecraft passes close to a body and observes it briefly without entering orbit, as New Horizons did at Pluto in 2015.

Focal length Odak uzaklığı

The distance from a lens or mirror to the point where parallel rays converge. In a telescope it sets the image scale and, with the eyepiece, the magnification.

Focal ratio (f-number) Odak oranı (f-sayısı)

The focal length divided by the aperture, written for example as f/5. Lower focal ratios give wider fields and reach a given surface brightness in shorter photographic exposures.

Footprint Kapsama alanı (ayak izi)

The area on Earth that a satellite's antenna can serve or its sensor can see. A geostationary satellite's global beam can view roughly a third of the planet's surface.

Formation flying Formasyon uçuşu

Two or more spacecraft flying together while precisely holding their relative distance and position. Twin satellites such as GRACE measured Earth's gravity field this way.

Four forces of flight Uçuşun dört kuvveti

Lift, weight, thrust and drag acting on an aircraft in flight; in straight, level, unaccelerated flight lift equals weight and thrust equals drag.

Frame dragging (Lense–Thirring effect) Çerçeve sürüklemesi (Lense–Thirring etkisi)

The dragging of spacetime around a rotating massive body in the direction of its spin; around Earth the effect was measured by Gravity Probe B and the LAGEOS satellites.

Fraunhofer lines Fraunhofer çizgileri

The hundreds of dark absorption lines in the Sun's spectrum. Joseph von Fraunhofer catalogued them in detail in 1814, and they were later traced to specific elements.

Free-space path loss (FSPL) Serbest uzay yol kaybı

The weakening of a radio wave as its energy spreads over an ever larger area in empty space. It grows with the square of distance and frequency and is the largest loss in a link budget.

Freeze-dried food Dondurularak kurutulmuş yiyecek

Space food lightened by removing water under vacuum while frozen, then prepared by adding hot or cold water before eating.

Frost line (snow line) Kar çizgisi (donma çizgisi)

The distance in a planet-forming disc beyond which it is cold enough for volatiles like water to condense into ice. The extra solid material beyond it allowed giant planets to form.

Full authority digital engine control (FADEC) FADEC

A digital system that continuously adjusts fuel flow and other engine parameters from sensor data, carrying out the pilot's thrust lever commands as efficiently and safely as possible.

Full Moon Dolunay

The phase when the Moon is on the opposite side of Earth from the Sun and its Earth-facing side appears fully lit. Lunar eclipses happen only at full moon.

Full-flow staged combustion Tam akışlı kademeli yanma

An advanced cycle in which all the fuel passes through a fuel-rich preburner and all the oxidizer through an oxidizer-rich one. SpaceX's Raptor is the first such engine to fly.

Fuselage Gövde (füzelaj)

The main structural body of an aircraft, housing the cockpit, passenger cabin and cargo, to which the wings and tail are attached.

G

G-load G yükü

The acceleration experienced by the crew during launch and re-entry, expressed in multiples of Earth's gravity; it places heavy strain on the body.

Gaganyaan Gaganyaan

The human spaceflight programme of the Indian Space Research Organisation (ISRO), which aims to carry a three-person crew into low Earth orbit.

Galactic bulge Galaksi şişkinliği

The dense, roughly spherical concentration of stars at the centre of a spiral galaxy. It is made mostly of old stars and surrounds the central black hole.

Galactic Center Galaksi merkezi

The rotational centre of the Milky Way, about 26,000 light-years away towards Sagittarius. Thick dust means it is best studied in infrared, radio and X-rays.

Galactic coordinate system Galaktik koordinat sistemi

A coordinate system based on the plane of the Milky Way, with zero longitude pointing towards the galactic centre; positions are given as galactic longitude (l) and latitude (b).

Galactic disk Galaksi diski

The flat, rotating component of a spiral galaxy where most stars, gas and dust are concentrated. The Sun lies in the Milky Way's disk about 26,000 light-years from the centre.

Galactic halo Galaksi halesi

A roughly spherical region enveloping a galaxy, containing sparse old stars, globular clusters and most of its dark matter. It extends far beyond the disk.

Galaxy Galaksi (gökada)

A vast system of millions to trillions of stars, together with gas, dust and dark matter, bound by gravity. The observable universe is estimated to contain hundreds of billions of them.

Galaxy cluster Galaksi kümesi

A gravitationally bound collection of hundreds to thousands of galaxies, the largest bound structures in the universe. Most of their mass is dark matter and hot gas.

Galaxy collision Galaksi çarpışması

An encounter in which two or more galaxies interact gravitationally and pass through each other. Stars rarely collide, but gas is compressed and bursts of star formation follow.

Galaxy filament Galaksi ipliği

Long, thread-like structures of galaxies and gas, hundreds of millions of light-years in length, that link clusters in the cosmic web. They are among the largest known structures.

Galaxy formation and evolution Galaksi oluşumu ve evrimi

The field studying how galaxies are born as gas cools and condenses in dark matter haloes, and how they change over time through mergers and star formation.

Galaxy group Galaksi grubu

A small gravitationally bound collection of up to a few dozen galaxies, smaller and less massive than a galaxy cluster.

Galaxy merger Galaksi birleşmesi

The process by which two colliding galaxies combine into one. Mergers of similar-mass spirals often produce an elliptical galaxy.

Galaxy rotation curve Galaksi dönme eğrisi

A plot of how fast stars and gas orbit as a function of distance from a galaxy's centre. Speeds that stay roughly flat far out, instead of falling, are key evidence for dark matter.

Gale Crater Gale krateri

A crater about 154 km across on Mars with a layered sedimentary mountain, Aeolis Mons (Mount Sharp), at its centre. The Curiosity rover has worked there since 2012.

Galilean moons Galileo uyduları

Jupiter's four large moons, discovered by Galileo Galilei in 1610: Io, Europa, Ganymede and Callisto. They can be seen with binoculars or a small telescope.

Galileo Galileo

The European Union's civilian-controlled global navigation satellite system. Its satellites orbit at about 23,200 km, and it has been providing services since 2016.

Gamma ray Gama ışını

The shortest-wavelength, highest-energy form of electromagnetic radiation. It comes from the most violent events, such as supernovae, pulsars, active galactic nuclei and gamma-ray bursts.

Gamma-ray burst (GRB) Gama ışını patlaması

The most powerful electromagnetic explosions known, seen in distant galaxies and lasting from milliseconds to minutes. Long ones come from collapsing massive stars, short ones from neutron star mergers.

Ganymede Ganymede (Ganimed)

The largest moon of Jupiter and of the Solar System, bigger even than Mercury. It is the only moon known to generate its own magnetic field and is the main target of ESA's JUICE mission.

Gas giant Gaz devi

A giant planet composed mostly of hydrogen and helium, with no well-defined solid surface. Jupiter and Saturn are the Solar System's two examples.

Gas-generator cycle Gaz üreteci çevrimi

An engine cycle in which a small share of propellant is burned in a separate generator to spin the turbine, and that gas is then dumped overboard. It is simple and reliable; Merlin and F-1 use it.

Geminids Geminidler

One of the year's richest meteor showers, peaking in mid-December. Unusually, its parent is the asteroid 3200 Phaethon rather than a comet; its radiant is in Gemini.

General relativity Genel görelilik

Einstein's 1915 theory describing gravity as the curvature of spacetime by mass and energy; it predicts black holes and gravitational waves.

Geomagnetic storm Jeomanyetik fırtına

A temporary disturbance of the magnetosphere caused by strong energy input from the solar wind or a CME; it spreads auroras and can affect satellites and power grids.

Geomagnetically induced current (GIC) Jeomanyetik olarak indüklenen akım

Current driven in long conductors such as power lines and pipelines by rapidly changing magnetic fields during a geomagnetic storm; it can damage transformers.

Geostationary orbit (GEO) Yer durağan yörünge

A circular geosynchronous orbit in the equatorial plane about 35,786 km above the surface. A satellite here appears fixed in the sky to ground observers; the Türksat fleet operates in GEO.

Geostationary transfer orbit (GTO) Yer durağan transfer yörüngesi

An elliptical intermediate orbit with a low perigee and an apogee near geostationary altitude. Communication satellites are usually released here and circularise their orbits with their own engines.

Geosynchronous orbit (GSO) Yer eşzamanlı yörünge

An orbit whose period equals one sidereal day, about 23 hours 56 minutes, so the satellite returns to the same point in the sky at the same time each day.

Giant star Dev yıldız

A star that, after exhausting core hydrogen, has swollen to become much larger and brighter than a main-sequence star of the same temperature. Its luminosity class is III.

Giant-impact hypothesis Dev çarpışma hipotezi

The leading theory that the Moon formed from debris thrown out when a Mars-sized body, called Theia, collided with the young Earth about 4.5 billion years ago.

Gimbal Gimbal (motor yalpalığı)

A pivoting mount that lets an engine swivel a few degrees, redirecting thrust to steer the vehicle. It is moved by hydraulic or electric actuators.

Glide ratio Süzülme oranı

The horizontal distance an unpowered aircraft covers for each unit of height lost; at 1:15, for example, one kilometre of altitude yields fifteen kilometres of travel.

Global Positioning System (GPS) Küresel Konumlama Sistemi

The United States' satellite navigation system, built on at least 24 satellites in six orbital planes at about 20,200 km altitude. It reached full operational capability in 1995.

Globular cluster Küresel küme

A tightly bound spherical cluster of tens of thousands to millions of old stars. About 150 are known in the Milky Way's halo, most older than 10 billion years.

GLONASS GLONASS

Russia's global navigation satellite system. Its satellites orbit at about 19,100 km in three orbital planes and give good coverage at high latitudes.

Go-around Pas geçme

Abandoning an approach when a safe landing cannot be completed and climbing away, followed by another approach or diversion to an alternate.

Go-To mount Go-To kundak

A computer-controlled motorised mount that finds, slews to and tracks an object chosen from its database. It must first be aligned on a few stars.

Graveyard orbit Mezar yörüngesi

An orbit a few hundred kilometres above geostationary orbit to which retired satellites are moved so they stay clear of working ones.

Gravitational collapse Kütleçekimsel çökme

The inward contraction of an object or cloud whose internal pressure can no longer resist its own gravity. It triggers both star formation and the creation of supernovae and black holes.

Gravitational constant (G) Evrensel kütleçekim sabiti (G)

The universal constant in Newton's law of gravitation that sets the strength of the attraction; its value is about 6.674 × 10⁻¹¹ N·m²/kg².

Gravitational lensing Kütleçekimsel merceklenme

The bending of light from a background source by an intervening mass, which can magnify, multiply or distort its image. Predicted by general relativity, it is used to map dark matter.

Gravitational microlensing Kütleçekimsel mikromercekleme

A planet-detection method that uses the brief brightening of a background star as a foreground star and its planet bend its light by gravity.

Gravitational redshift Kütleçekimsel kırmızıya kayma

The shift of light to longer wavelengths as it climbs out of a strong gravitational field and loses energy; it has been measured in white dwarf spectra and in laboratory experiments on Earth.

Gravitational singularity Kütleçekimsel tekillik

The point at a black hole's center where, according to general relativity, density and spacetime curvature become infinite. Its true nature remains unclear without a theory of quantum gravity.

Gravitational time dilation Kütleçekimsel zaman genişlemesi

The slower running of clocks in stronger gravitational fields than in weaker ones; combined with the speed effect, it requires GPS satellites to be corrected by about 38 microseconds per day.

Gravitational wave Kütleçekim dalgası

Ripples in spacetime produced by accelerating masses and travelling at the speed of light. Einstein predicted them in 1916; LIGO made the first direct detection in 2015.

Gravity (gravitation) Kütleçekimi

The fundamental interaction by which all objects with mass attract one another; it governs planetary orbits, tides and the formation of stars.

Gravity assist (slingshot manoeuvre) Kütleçekim yardımı (sapan etkisi)

Using a close flyby of a planet so its gravity changes a spacecraft's direction and speed relative to the Sun; the Voyager probes reached the outer planets this way.

Gravity loss Kütleçekim kaybı

The delta-v lost because part of the thrust during ascent is spent simply fighting gravity. A high thrust-to-weight ratio and a quick turn to horizontal reduce it.

Gravity tractor Kütleçekimsel çekici

A contact-free deflection method in which a spacecraft hovers near an asteroid for a long time, slowly altering its orbit with the craft's own slight gravity.

Gravity turn Kütleçekim dönüşü

An ascent profile in which the rocket pitches over slightly after a vertical climb and lets gravity gradually tip it toward horizontal. It reduces aerodynamic loads and wasted propellant.

Great Red Spot Büyük Kırmızı Leke

A giant anticyclonic storm in Jupiter's southern hemisphere that has lasted for centuries at least. Though it has shrunk in recent decades, it is still wider than Earth.

Great-circle route Büyük daire rotası

The shortest path between two points on a sphere's surface, which is why long-haul flights look curved towards the poles on a flat map.

Gregorian calendar Gregoryen takvim (Miladi takvim)

The solar calendar introduced by Pope Gregory XIII in 1582, correcting the Julian calendar's leap-year rule; it is now the world's most widely used civil calendar.

Grid fins Izgara kanatçıklar

Lattice-shaped steerable aerodynamic surfaces near the top of a returning stage. They steer it during descent through the atmosphere; Falcon 9 and Super Heavy use them.

Gridded ion thruster İyon motoru

An electric thruster that ionizes a gas and accelerates the ions between charged grids to very high exhaust speeds. The Dawn probe reached Vesta and Ceres on xenon ion engines.

Ground control station (GCS) Yer kontrol istasyonu

The ground facility from which an unmanned aircraft's flight is planned, monitored and commanded, receiving imagery and telemetry over a data link.

Ground effect Yer etkisi

The rise in lift and fall in induced drag when a wing or rotor comes within about one span of the ground, because the surface weakens tip vortices and downwash.

Ground sample distance (GSD) Yer örnekleme aralığı

The ground distance between the centres of two adjacent pixels in an image. It serves as the practical measure of spatial resolution and depends on altitude and optics.

Ground segment Yer bölümü

The Earth-based part of a space system: ground stations, mission control, data-processing facilities and the networks linking them.

Ground speed Yer hızı

An aircraft's speed over the ground, found by combining true airspeed with the wind; a tailwind increases it and a headwind reduces it.

Ground station Yer istasyonu

An Earth facility with antennas, transceivers and tracking equipment for radio contact with spacecraft. It receives telemetry, sends commands and downloads mission data.

Ground track Yer izi

The path traced on Earth's surface by the point directly beneath a satellite. Because Earth rotates, each successive pass shifts westward.

Guiana Space Centre Guyana Uzay Merkezi

Europe's spaceport at Kourou, French Guiana, about 5° from the equator. Ariane and Vega rockets launch from here.

H II region H II bölgesi

A glowing region where hydrogen around young, hot O and B stars has been ionized. It marks recent star formation; the Orion Nebula is a typical example.

Habitable zone (Goldilocks zone) Yaşanabilir bölge (Goldilocks bölgesi)

The range of distances from a star at which a planet with a suitable atmosphere could keep liquid water on its surface.

Hall-effect thruster Hall etkili itici

An electric thruster that traps electrons in a magnetic field and uses the resulting electric field to accelerate ions. Starlink satellites use Hall thrusters running on krypton or argon.

Halley's Comet (1P/Halley) Halley Kuyruklu Yıldızı

The most famous naked-eye short-period comet, returning about every 76 years. Its last appearance was in 1986, and it is next due in 2061.

Hawking radiation Hawking ışıması

Radiation that, as Stephen Hawking predicted in 1974, black holes should slowly emit through quantum effects, gradually losing mass. It is extremely faint for stellar-mass black holes and has not yet been observed.

Head-up display (HUD) Baş üstü gösterge

A display that projects flight data onto a transparent screen in the pilot's line of sight, so information can be read while looking outside.

Heat shield Isı kalkanı

A protective layer, usually covering the vehicle's leading face, that shields it from heating of thousands of degrees during atmospheric entry. Apollo and Orion capsules use blunt ablative shields.

Heavy-lift launch vehicle Ağır yük roketi

A launch vehicle class able to place roughly 20 to 50 tonnes into low Earth orbit. Falcon Heavy and Delta IV Heavy fall into this class.

Helicopter Helikopter

A rotary-wing aircraft that gets both lift and thrust from an engine-driven main rotor, allowing vertical take-off, landing and hovering.

Heliopause Heliopoz

The edge of the heliosphere where solar-wind pressure balances that of the interstellar medium; Voyager 1 crossed it in 2012 and Voyager 2 in 2018.

Helioseismology Helyosismoloji

The study of the Sun's interior structure, temperature and rotation by measuring oscillations on its surface, much as seismology probes Earth's interior.

Heliosphere Heliosfer

The vast bubble, enclosing all the planets, in which the solar wind and the Sun's magnetic field push back the interstellar medium.

Helium flash Helyum parlaması

The runaway ignition of helium fusion within minutes in the degenerate core of a star below about 2 solar masses. The energy is absorbed inside the star and is not directly visible.

Herbig–Haro object Herbig–Haro nesnesi

A bright patch of shocked gas created where jets from a young star slam into surrounding material. They last only briefly, often a few thousand years.

Hertzsprung–Russell diagram (H–R diagram) Hertzsprung–Russell diyagramı (HR diyagramı)

A plot of stellar luminosity against surface temperature or spectral type. Main-sequence stars, giants and white dwarfs fall into distinct regions on it.

High-energy astrophysics Yüksek enerji astrofiziği

The branch studying extreme phenomena such as black holes, neutron stars and supernovae through high-energy radiation and particles: X-rays, gamma rays, cosmic rays and neutrinos.

High-throughput satellite (HTS) Yüksek kapasiteli uydu

A communications satellite that uses many spot beams and frequency reuse to carry many times more data than conventional designs, with total capacity reaching hundreds of Gbit/s.

Highly elliptical orbit (HEO) Yüksek eliptik yörünge

A strongly eccentric orbit with a low perigee and a very high apogee. Because the satellite slows near apogee, it can linger over one region for many hours.

Hijri calendar Hicri takvim

A lunar calendar counted from the Hijra in 622, with 12 lunar months making a year of 354 or 355 days, so its months drift through the seasons.

Hill sphere Hill küresi

The approximate region in which a body orbiting a larger one can hold on to satellites with its own gravity; for Earth its radius is about 1.5 million km.

Hohmann transfer orbit Hohmann transfer yörüngesi

An elliptical orbit tangent to two coplanar circular orbits that moves a spacecraft between them with two engine burns; it is usually the most energy-efficient two-burn route.

Horizon problem Ufuk problemi

The puzzle that widely separated regions which should never have been in contact show almost identical CMB temperatures. Cosmic inflation is the leading proposed solution.

Horizontal branch Yatay kol

A roughly horizontal band on the H–R diagram formed by old, low-mass stars burning helium in their cores. It stands out clearly in globular cluster diagrams.

Horizontal coordinate system (alt-azimuth) Ufuk koordinat sistemi

A system based on the observer's local horizon that gives positions as altitude and azimuth; the coordinates change continuously with Earth's rotation and with the observer's location.

Horsehead Nebula Atbaşı Bulutsusu

A dark cloud of dust in Orion that forms a horse's-head silhouette against a glowing emission nebula behind it. It is a favorite target of amateur astrophotographers.

Hot Jupiter Sıcak Jüpiter

A gas giant orbiting very close to its star, usually in under 10 days, and extremely hot; the first exoplanet found around a Sun-like star was one.

Hot staging Sıcak ayrılma

A separation method in which the upper-stage engine fires before the lower stage has fully detached. It is traditional on Soviet rockets and has been used on Starship since 2023.

Hubble constant (H₀) Hubble sabiti

The present-day expansion rate of the universe, measured at about 67–73 km/s per megaparsec. It gives how much faster galaxies recede for each megaparsec of distance.

Hubble Deep Field Hubble Derin Alanı

A famous Hubble Space Telescope observation, first made in 1995, that imaged a tiny patch of sky with a long exposure and revealed thousands of distant galaxies.

Hubble tension Hubble gerilimi

The unresolved mismatch between the Hubble constant inferred from the early universe (CMB), about 67 km/s/Mpc, and local distance measurements giving about 73 km/s/Mpc.

Hubble tuning fork Hubble ayar çatalı

Edwin Hubble's 1926 morphological scheme, which arranges galaxies into ellipticals, lenticulars, spirals and barred spirals on a fork-shaped diagram.

Hubble–Lemaître law Hubble–Lemaître yasası

The relation stating that a distant galaxy's recession speed is proportional to its distance, v = H₀·d. It is the basic observational evidence that the universe is expanding.

Human centrifuge İnsan santrifüjü

A training device with a cabin on a rapidly spinning arm, used to accustom astronauts to the high accelerations of launch and re-entry.

Human Landing System (HLS) İnsan İniş Sistemi

The lander that will take Artemis astronauts from lunar orbit to the surface and back; NASA chose SpaceX's Starship and Blue Origin's Blue Moon for the job.

Human spaceflight İnsanlı uzay uçuşu

The general term for flights in which people travel into space as crew or passengers aboard a spacecraft; the first was Vostok 1 on 12 April 1961.

Hybrid rocket Hibrit roket

A rocket that uses a solid fuel with a liquid or gaseous oxidizer. Cutting off oxidizer flow shuts the motor down, and it is considered safer than a solid rocket.

Hydrazine Hidrazin

A toxic liquid, N₂H₄, used either as a monopropellant decomposed over a catalyst or as a hypergolic fuel with an oxidizer. It is common in satellite and spacecraft thrusters.

Hydrogen-alpha (Hα) filter Hidrojen-alfa filtresi

A narrowband filter passing hydrogen's red emission line at 656.3 nanometres. It is used to image emission nebulae and, in special designs, to observe solar prominences.

Hydrostatic equilibrium Hidrostatik denge

The balance in a star between gravity pulling inward and gas and radiation pressure pushing outward. It keeps the star at a stable size.

Hyperbolic trajectory Hiperbolik yörünge

An open orbit with eccentricity greater than 1, along which a body approaches the central mass once and leaves for good; interstellar visitors arrive on such paths.

Hypergolic propellant Hipergolik itken

A fuel-oxidizer pair that ignites spontaneously on contact, with no igniter needed. Hydrazine derivatives with nitrogen tetroxide are the classic example; toxic but storable.

Hypersonic flight Hipersonik uçuş

Flight at speeds generally above Mach 5, where aerodynamic heating, chemical breakdown of air and material endurance become the main engineering challenges.

Hyperspectral imaging Hiperspektral görüntüleme

Imaging that records a spectrum in hundreds of narrow, contiguous bands for every pixel, so materials such as minerals, crop diseases and pollutants can be identified by their spectral signatures.

I

Ice giant Buz devi

A giant planet that, besides hydrogen and helium, is rich in so-called 'ices' such as water, ammonia and methane. Uranus and Neptune fall into this class.

IceCube Neutrino Observatory IceCube Nötrino Gözlemevi

A neutrino telescope at the South Pole, made of thousands of light sensors embedded in a cubic kilometre of ice. It detects high-energy cosmic neutrinos.

Icing Buzlanma

The freezing of supercooled water droplets onto aircraft surfaces; it distorts the wing's shape, reducing lift while adding weight and drag.

Image stacking Görüntü yığma (istifleme)

Aligning and combining many frames of the same object to reduce noise and bring out faint detail. It is a core step in astrophotography processing.

Imaging atmospheric Cherenkov telescope (IACT) Atmosferik Çerenkov teleskobu

A ground-based telescope that detects the brief blue Cherenkov light from particle showers created when very-high-energy gamma rays hit the atmosphere. H.E.S.S. and MAGIC are examples.

İMECE İMECE

A domestically developed Earth-observation satellite from TÜBİTAK Space with sub-metre resolution. It was launched by Falcon 9 into sun-synchronous orbit in April 2023.

Impact crater Çarpma krateri

A bowl-shaped depression formed when an asteroid, comet or meteoroid strikes a surface at high speed. The Moon, Mercury and many moons are covered in them.

In-orbit propellant transfer Yörüngede itken aktarımı

Moving propellant from a tanker vehicle to another vehicle in orbit. Starship's Moon and Mars missions are planned to rely on refuelling this way.

In-situ resource utilization (ISRU) Yerinde kaynak kullanımı

Making supplies such as oxygen, water or propellant from local materials on the Moon or Mars instead of hauling them from Earth; MOXIE on Perseverance produced oxygen from Martian air.

Induced drag İndüklenmiş sürükleme

Drag that arises as a by-product of producing lift, linked to wingtip vortices; it is greatest at low speed and high angle of attack.

Inflatable module Şişirilebilir modül

A soft-walled habitat that launches folded and expands with air once in orbit; BEAM, added to the ISS in 2016, is an experimental example.

Infrared (IR) Kızılötesi

Radiation with wavelengths longer than visible red light and shorter than microwaves. It lets astronomers see through dust clouds and detect the heat of cool objects.

Infrared astronomy Kızılötesi astronomi

The branch of astronomy that studies objects in infrared light. It reveals star-forming regions, cool bodies and very distant, redshifted galaxies.

Ingenuity Ingenuity

The small test helicopter that travelled to Mars with Perseverance. On 19 April 2021 it made the first powered, controlled flight on another planet and went on to complete 72 flights.

Injector Enjektör

The engine component that sprays fuel and oxidizer into the chamber in the right proportion and as fine droplets so they mix well. Its design is critical to combustion stability.

Instrument flight rules (IFR) Aletli uçuş kuralları

Rules under which an aircraft is flown by reference to instruments and under air traffic control guidance without needing outside visibility; commercial airline flights operate under them.

Instrument landing system (ILS) Aletli iniş sistemi

A system that guides aircraft precisely to the runway in poor visibility using radio beams: a localizer for the centreline and a glide slope typically angled at 3°.

Integral field spectrograph İntegral alan tayfçekeri

A spectrograph that records a separate spectrum for every point in the image, capturing spatial and spectral information at once. Webb's NIRSpec and MIRI include this mode.

Inter-satellite link (ISL) Uydular arası bağlantı

Direct data exchange between satellites by radio or laser, without routing through a ground station. Starlink satellites use laser links to form a network in space.

Interferometric SAR (InSAR) İnterferometrik SAR

A technique comparing the phase of SAR images taken at different times to measure ground uplift or subsidence at millimetre-to-centimetre scale. It is used to study earthquakes and landslides.

Interferometry İnterferometri (girişimölçer)

Combining signals from several widely separated telescopes to achieve resolution approaching that of a single telescope as large as the distance between them.

Intergalactic medium (IGM) Galaksiler arası ortam

The very thin gas, mostly ionized hydrogen and helium, filling the space between galaxies. It holds most of the universe's ordinary matter.

International Civil Aviation Organization (ICAO) ICAO

The United Nations specialised agency, created by the 1944 Chicago Convention and based in Montreal, that sets international civil aviation standards.

International Space Station (ISS) Uluslararası Uzay İstasyonu (UUİ)

A station run jointly by the US, Russia, Europe, Japan and Canada, orbiting at roughly 400 km; it has been continuously crewed since November 2000.

International Standard Atmosphere (ISA) Uluslararası standart atmosfer

A reference atmosphere assuming 15 °C and 1013.25 hPa at sea level, with temperature falling by 6.5 °C per kilometre up to 11 km.

International Telecommunication Union (ITU) Uluslararası Telekomünikasyon Birliği (ITU)

The Geneva-based UN agency that coordinates and records the radio frequencies used by satellites and positions in geostationary orbit.

Interplanetary magnetic field (IMF) Gezegenlerarası manyetik alan (GMA)

The Sun's magnetic field carried into space by the solar wind; when it points southward it couples more easily with Earth's field and raises storm risk.

Interstellar dust Yıldızlararası toz

Grains of silicate and carbon, mostly smaller than a micrometer, scattered between the stars. They absorb and scatter starlight and are the raw material for planets.

Interstellar extinction Yıldızlararası sönümleme

The dimming of starlight as dust along its path absorbs and scatters it. It is strongest in the galactic plane and must be corrected for when measuring distances.

Interstellar medium Yıldızlararası ortam

The gas, dust, cosmic rays and magnetic fields that fill the space between stars. By mass it is about 99 percent gas and 1 percent dust.

Interstellar object Yıldızlararası cisim

A body formed around another star that passes through the Solar System on an unbound, hyperbolic path. Known examples are 1I/ʻOumuamua, 2I/Borisov and 3I/ATLAS.

Intracluster medium (ICM) Kümeler arası ortam

The thin plasma, at tens of millions of degrees, filling the space between galaxies in a cluster. It glows in X-rays and holds most of the cluster's ordinary matter.

Io Io

The innermost Galilean moon of Jupiter and the most volcanically active body in the Solar System. Its volcanism is driven by tidal heating from Jupiter and its neighbouring moons.

Ion tail (gas tail) İyon kuyruğu (gaz kuyruğu)

A straight, often bluish tail of gas ionised by solar ultraviolet light and swept outward by the solar wind. It always points directly away from the Sun.

Ionosphere İyonosfer

The part of the upper atmosphere, roughly 60–1,000 km up, ionized by solar radiation; it reflects radio waves and responds directly to space weather.

Iridium–Kosmos collision Iridium–Kosmos çarpışması

The first accidental collision between two intact satellites, when the active Iridium 33 and the defunct Russian Kosmos 2251 hit each other over Siberia on 10 February 2009.

Iron meteorite Demir göktaşı

A meteorite made mostly of iron-nickel alloy, thought to come from the cores of shattered asteroids. When cut and etched with acid it reveals a Widmanstätten pattern.

Irregular galaxy Düzensiz galaksi

A galaxy with no defined spiral or elliptical shape, often small and gas-rich. The Large and Small Magellanic Clouds are commonly cited examples.

Istanbul Observatory of Taqi al-Din İstanbul Rasathanesi (Takiyüddin Rasathanesi)

An Ottoman observatory founded in Istanbul in 1577 under Taqi al-Din during the reign of Murad III, equipped with advanced instruments for its time but demolished in 1580.

J

Jamming and spoofing Sinyal karıştırma ve aldatma

Blinding GNSS receivers with strong noise (jamming) or tricking them into a false position with counterfeit satellite signals (spoofing). Both pose serious safety threats to aviation and shipping.

Jeans mass Jeans kütlesi

The minimum mass a gas cloud needs to collapse under its own gravity. The threshold falls as the cloud becomes colder and denser.

Jet engine Jet motoru

A reaction engine that draws in and compresses air, burns it with fuel and expels a high-speed exhaust jet to produce thrust; turbojets, turbofans and ramjets belong to this class.

Jet fuel (Jet A-1) Jet yakıtı (Jet A-1)

Kerosene-based fuel used in aircraft gas-turbine engines; the Jet A-1 grade is produced with a maximum freezing point of −47 °C.

Jet stream Jet akımı

A narrow band of strong westerly winds near the tropopause that can reach several hundred kilometres per hour, shortening eastbound flights.

Jezero Crater Jezero krateri

A crater about 45 km wide on Mars that once held a lake and a river delta. NASA's Perseverance rover landed there in February 2021.

Julian date (JD) Jülyen günü

A continuous count of days since noon on 1 January 4713 BC in the Julian calendar, used by astronomers to compare events across different calendars easily.

Jupiter Jüpiter

The largest planet in the Solar System, with more than two and a half times the combined mass of all the other planets. It is a gas giant with a large family of moons.

K

Ka band Ka bandı

The microwave band of roughly 26.5–40 GHz. Its wide bandwidth suits high-throughput internet satellites and fast science downlinks, though it is sensitive to rain fade.

Kandilli Observatory Kandilli Rasathanesi

An institution founded in Istanbul in 1868 as the Imperial Observatory for meteorology, later moved to Kandilli, which today works in seismology and astronomy.

Kennedy Space Center (KSC) Kennedy Uzay Merkezi

NASA's launch centre on Merritt Island, Florida. Apollo, Space Shuttle and Artemis missions have lifted off from its Pads 39A and 39B.

Kepler space telescope Kepler Uzay Teleskobu

A NASA observatory that, from 2009 to 2018, found thousands of exoplanets with the transit method and showed that Earth-sized planets are common.

Kepler's first law (law of ellipses) Kepler'in birinci yasası

The law stating that planets orbit the Sun in ellipses, with the Sun at one focus.

Kepler's second law (law of equal areas) Kepler'in ikinci yasası

The law stating that a line joining a planet to the Sun sweeps out equal areas in equal times, so planets move faster when closer to the Sun.

Kepler's third law (harmonic law) Kepler'in üçüncü yasası

The law stating that the square of a planet's orbital period is proportional to the cube of its orbit's semi-major axis (T² ∝ a³).

Kessler syndrome Kessler sendromu

The scenario, predicted by Donald Kessler in 1978, in which crowded orbits make collisions generate debris that triggers a cascade of further collisions.

Kibo (Japanese Experiment Module) Kibo

Japan's (JAXA) experiment module on the ISS; it is the station's largest single module and includes an exposed platform for experiments in open space.

Kilonova Kilonova

An explosion powered by radioactive r-process elements forged when two neutron stars, or a neutron star and a black hole, merge. The first definitive one was seen in 2017 with GW170817.

Kinetic impactor Kinetik çarpıştırıcı

Deflecting an asteroid by ramming a spacecraft into it at high speed, a technique proven feasible by the DART mission.

Kirkwood gaps Kirkwood boşlukları

Sparsely populated zones in the asteroid belt where orbital periods would form simple ratios with Jupiter's, such as 3:1, 5:2 or 2:1. Jupiter's repeated tugs destabilise these orbits.

Kp index Kp indeksi

A global 0–9 scale of geomagnetic disturbance measured over three-hour intervals; values of 5 or higher count as a geomagnetic storm.

Ku band Ku bandı

The microwave band of roughly 12–18 GHz, the main band for direct-to-home satellite TV and small-dish VSAT services. It suffers more from rain than C band.

Kuiper belt Kuiper kuşağı

A disc-shaped zone of icy small bodies beyond Neptune's orbit, roughly 30–50 AU from the Sun. Pluto and several other dwarf planets reside there.

Kármán line Kármán çizgisi

The widely accepted boundary of space, 100 km above sea level. In the US, an 80 km (50 mile) threshold is used for awarding astronaut wings.

L band L bandı

The microwave band of roughly 1–2 GHz. Little affected by the atmosphere, it carries GNSS signals, mobile satellite telephony and some SAR missions.

Lagrange point L2 L2 Lagrange noktası

The equilibrium point of the Sun–Earth system about 1.5 million km beyond Earth on the side away from the Sun; telescopes such as James Webb and Gaia operate there.

Lagrange points Lagrange noktaları

Five points (L1–L5) where the gravity of two large bodies balances the effects of rotation so that a small object can keep a fixed position relative to them; L4 and L5 are stable, the rest unstable.

Lambda-CDM model (ΛCDM) ΛCDM modeli

The standard model of cosmology, containing a cosmological constant (dark energy) and cold dark matter. It fits CMB, galaxy-clustering and supernova data with only a few parameters.

Lander İniş aracı

A spacecraft that makes a controlled touchdown on a body's surface and stays put to take measurements, such as InSight on Mars and China's Chang'e landers on the Moon.

Landing burn İniş ateşlemesi

The final engine firing a stage makes as it approaches the landing site, bringing its speed close to zero. Falcon 9 usually does it on a single engine.

Landing gear İniş takımı

The wheels, shock absorbers and brakes that support an aircraft on the ground and during take-off, taxi and landing; on most aircraft it retracts in flight.

Landing legs İniş bacakları

Folding supports that a stage deploys at the end of its descent to absorb the load at touchdown. Falcon 9 uses four carbon-fibre legs.

Laniakea Supercluster Laniakea Üstkümesi

The supercluster that includes the Milky Way, estimated to hold about 100,000 galaxies across some 500 million light-years. It was defined in 2014 from galaxy motions.

Large-scale structure Büyük ölçekli yapı

The distribution of matter and galaxies on scales larger than millions of light-years: clusters, superclusters, filaments and voids. It is mapped with galaxy redshift surveys.

Laser guide star Lazer kılavuz yıldız

An artificial reference point made by exciting sodium atoms high in the atmosphere with a laser, used by adaptive optics when no bright natural star is available.

Laser Interferometer Gravitational-Wave Observatory (LIGO) LIGO

A US gravitational-wave observatory of two laser interferometers with 4 km arms. In 2015 it detected waves from merging black holes, a discovery honoured with the 2017 Nobel Prize in Physics.

Late Heavy Bombardment Geç Ağır Bombardıman

A proposed period roughly 4.1 to 3.8 billion years ago when impacts in the inner Solar System sharply increased. Suggested by lunar samples, its reality is still debated.

Latency Gecikme süresi

The time a signal takes to travel from source to destination. A single ground–satellite–ground hop via GEO takes about 240 milliseconds; LEO networks cut this to tens of milliseconds.

Launch escape system Fırlatma kaçış sistemi

An emergency system that fires powerful motors to pull the capsule rapidly away from a failing rocket and lower it by parachute; it may be a tower or engines built into the capsule.

Launch pad Fırlatma rampası

The ground facility where a rocket is erected, fuelled and launched. It includes a tower, flame trench, propellant storage and water deluge systems.

Launch scrub Fırlatma ertelemesi

The calling off of a launch attempt, postponing it to another time, because of weather, a technical problem or range restrictions.

Launch vehicle Fırlatma aracı (fırlatıcı)

A rocket system used to carry payloads from the ground into space or orbit. By capacity it is classed as small, medium, heavy or super heavy.

Launch window Fırlatma penceresi

The span of time in which a rocket must lift off to reach its intended orbit or target. It can be seconds long for space station missions and weeks long for planetary ones.

Leap second Artık saniye

A one-second adjustment occasionally added to UTC to keep it in step with Earth's irregular, slowing rotation; 27 have been inserted since 1972.

Leap year Artık yıl

A 366-day year with an extra day in February to keep the calendar aligned with the tropical year; in the Gregorian calendar it falls in years divisible by 4, except century years not divisible by 400.

Lenticular galaxy Mercek biçimli galaksi

A galaxy with a disk and central bulge but no clear spiral arms. Labelled S0 in the Hubble scheme, it sits between ellipticals and spirals.

Leonids Leonidler

A meteor shower in mid-November produced by Comet 55P/Tempel–Tuttle. Roughly every 33 years it can erupt into meteor storms of thousands of meteors per hour.

Liability Convention Sorumluluk Sözleşmesi

A 1972 UN convention holding the launching state liable for damage caused by its space objects and setting out how compensation is claimed.

Lidar Lidar

An active sensing method that fires laser pulses and times their reflections to measure distance. From orbit it maps ice thickness, forest height and terrain topography.

Life support system Yaşam destek sistemi

The collection of systems on a spacecraft that keeps the crew alive by supplying breathable air, suitable pressure and temperature, water and waste management.

Lifeboat (crew return vehicle) Cankurtaran aracı

A spacecraft kept docked at a station so the crew can abandon it and return to Earth quickly in an emergency; on the ISS, docked Soyuz and Crew Dragon vehicles fill this role.

Lift Kaldırma kuvveti

The force produced perpendicular to the oncoming airflow by pressure differences around a surface such as a wing; it balances the aircraft's weight and keeps it airborne.

Lift-to-drag ratio (L/D) Kaldırma/sürükleme oranı

The ratio of lift to drag an aircraft produces, a key measure of aerodynamic efficiency; around 15–20 for modern airliners and over 50 for high-performance gliders.

Lifting entry Kaldırmalı giriş

Atmospheric entry in which lift from the vehicle's or capsule's shape lengthens and steers the descent. It lowers deceleration loads and improves landing accuracy.

Light curve Işık eğrisi

A graph showing how an object's brightness changes over time. It is the basic data for studying variable stars, supernovae and exoplanet transits.

Light pollution Işık kirliliği

Excessive or misdirected artificial lighting that brightens the night sky and hides faint stars. Besides hindering observation, it harms wildlife and wastes energy.

Light-gathering power Işık toplama gücü

How much more light a telescope collects than the eye's pupil; it scales with the aperture's area, the square of its diameter. Doubling the diameter quadruples the light.

Light-year (ly) Işık yılı

The distance light travels in a vacuum in one Julian year, about 9.46 trillion kilometres; it is a unit of distance, not time.

Limiting magnitude Sınır kadir

The magnitude of the faintest object visible with a given eye, telescope or camera. Under very dark skies the naked-eye limit is roughly magnitude 6 to 6.5.

Link budget Bağlantı bütçesi

A tally that starts from transmitter power, adds antenna gains and subtracts all losses to find the signal level at the receiver, showing whether a link will close with enough margin.

Liquid cooling and ventilation garment Sıvı soğutmalı iç giysi

A close-fitting undergarment worn beneath a spacesuit, carrying a web of thin tubes through which water flows to draw away body heat.

Liquid hydrogen (LH2) Sıvı hidrojen (LH2)

The rocket fuel that delivers the highest chemical specific impulse, liquefied at about −253 °C. Its very low density demands large tanks; RS-25 and Vulcain burn it.

Liquid oxygen (LOX) Sıvı oksijen (LOX)

The most widely used rocket oxidizer: oxygen liquefied at about −183 °C. It is paired with kerosene, hydrogen and methane.

Liquid-propellant rocket Sıvı yakıtlı roket

A rocket that carries fuel and oxidizer as liquids in separate tanks and feeds them to the chamber. It can be throttled, shut down and restarted, and offers high specific impulse.

Load factor (g) Yük faktörü

The ratio of the lift generated by the wings to the aircraft's weight, expressed in g; in a level turn at 60° of bank it is 2 g.

Local Group Yerel Grup

The galaxy group containing the Milky Way, Andromeda, Triangulum and dozens of dwarf galaxies. It spans about 10 million light-years.

Long-duration mission Uzun süreli görev

A mission in which astronauts stay in space for months, sometimes close to a year, yielding valuable data on how the human body adapts.

Long-period comet Uzun dönemli kuyruklu yıldız

A comet with an orbital period longer than 200 years, sometimes millions of years. Arriving from all directions, they are thought to originate in the Oort cloud.

Longitude of the ascending node (RAAN) Çıkış düğümü boylamı

The angle measured in the reference plane from a reference direction, usually the vernal equinox, to the orbit's ascending node; it fixes the orientation of the orbital plane in space.

Lookback time Bakış zamanı

The time light from a distant object took to reach us, telling how far into the past we see it. For redshift z = 1, it is about 7.7 billion years.

Low Earth orbit (LEO) Alçak Dünya yörüngesi

Orbits between roughly 160 and 2,000 km altitude. The ISS, Starlink and many Earth-observation satellites circle the planet here about every 90–120 minutes.

Lucky imaging Şanslı görüntüleme

Shooting thousands of very short frames and combining only the sharpest ones, taken when the atmosphere was momentarily steady. It is widely used in planetary photography.

Luminosity Işıtma gücü (ışınım gücü)

The total energy a star radiates per unit time across all wavelengths. It does not depend on distance and is usually quoted in units of the Sun's luminosity.

Luminosity class Işıtma sınıfı

A Roman-numeral scale that separates stars of the same spectral type by size and luminosity: I for supergiants, III for giants, IV for subgiants and V for main-sequence dwarfs.

Luminous blue variable (LBV) Parlak mavi değişen (LBV)

A massive, unstable and extremely luminous star showing irregular brightness changes and occasional huge mass ejections. Eta Carinae and P Cygni are examples.

Lunar base Ay üssü

A permanent facility planned on the lunar surface, with habitats, power, communications and vehicles, so astronauts can stay for weeks or months.

Lunar Gateway Ay Geçidi

A small space station planned under Artemis for a long, elliptical orbit around the Moon, meant to serve astronauts as a staging point and research outpost.

Lunar highlands Ay yüksek arazileri

The bright, heavily cratered regions of the Moon, older than the maria. They consist largely of anorthosite, a rock rich in calcium feldspar.

Lunar libration Ay librasyonu

The slight apparent wobble of the Moon as seen from Earth, caused by its elliptical, tilted orbit. Over time it lets us see about 59% of the lunar surface.

Lunar mare Ay denizi (mare)

A broad, dark plain on the Moon formed by basalt lava that flooded ancient impact basins. Early observers mistook them for seas; the plural is maria.

Lunar Module (LM) Ay modülü

The two-stage Apollo vehicle that carried two astronauts from lunar orbit to the surface and back; the descent stage stayed on the Moon while the ascent stage lifted off.

Lunar phases Ay'ın evreleri

The changing appearance of the Moon as we see more or less of its sunlit half: new moon, first quarter, full moon and last quarter. A full cycle takes about 29.5 days.

Lunar Roving Vehicle (LRV) Ay gezgini aracı

A battery-powered, two-seat electric car that let astronauts on Apollo 15, 16 and 17 travel many kilometres across the lunar surface.

M

M-type asteroid M tipi asteroit

An asteroid class with metal-like spectra, some of which may be iron-nickel remnants of shattered protoplanet cores. 16 Psyche is the best-known example.

Mach number Mach sayısı

The ratio of an object's speed to the local speed of sound; at sea level and 15 °C, Mach 1 is about 340 m/s, or roughly 1,225 km/h.

Magellanic Clouds Macellan Bulutları

Two irregular dwarf galaxies orbiting the Milky Way, the Large and Small Magellanic Clouds. Visible to the naked eye from the Southern Hemisphere, they lie about 160,000 and 200,000 light-years away.

Magnetar Magnetar

A neutron star with a magnetic field hundreds to a thousand times stronger than that of an ordinary neutron star. Upheavals in its field can unleash powerful bursts of X-rays and gamma rays.

Magnetic reconnection Manyetik yeniden bağlanma

The breaking and rejoining of oppositely directed magnetic field lines, releasing stored energy as heat and fast particles; it powers flares and auroras.

Magnetopause Manyetopoz

The outer boundary of the magnetosphere where Earth's magnetic pressure balances the solar wind; on the dayside it usually lies about 10 Earth radii away.

Magnetorquer Manyetik tork çubuğu

A coil or rod that, when energised, interacts with Earth's magnetic field to produce torque. It is common on small LEO satellites and for dumping momentum stored in reaction wheels.

Magnetosphere Manyetosfer

The region dominated by a planet's magnetic field, shielding Earth from most of the solar wind; it is compressed on the dayside and stretched into a long tail on the nightside.

Magnification Büyütme

How many times larger an object appears through a telescope than to the naked eye. It equals the telescope's focal length divided by the eyepiece's focal length.

Magnitude Kadir (parlaklık derecesi)

A logarithmic scale of celestial brightness in which smaller numbers mean brighter objects; a difference of 5 magnitudes corresponds to exactly a factor of 100 in brightness.

Main engine cutoff (MECO) Ana motor kesmesi (MECO)

The planned shutdown of the first-stage or core-stage engines. Stage separation usually follows.

Main rotor Ana rotor

The horizontally spinning assembly of airfoil-shaped blades on top of a helicopter that produces lift, thrust and control forces.

Main sequence Anakol

The diagonal band on the H–R diagram occupied by stars fusing hydrogen into helium in their cores. Stars spend about 90 percent of their lives here; the Sun is a main-sequence star.

Main-sequence turnoff Anakoldan ayrılma noktası

The point on a cluster's H–R diagram where stars begin to leave the main sequence. The mass of stars at this point is used to work out the cluster's age.

Makemake Makemake

A dwarf planet discovered in 2005 and one of the brightest objects in the Kuiper belt. Its surface is coated in frozen methane, ethane and other ices.

Maksutov–Cassegrain telescope Maksutov-Cassegrain teleskobu

A catadioptric telescope with a thick, curved meniscus corrector lens at the front. Its sharp, high-contrast views make it a favourite for observing the Moon and planets.

Manned Maneuvering Unit (MMU) İnsanlı Manevra Birimi

A backpack driven by nitrogen-gas thrusters that let an astronaut move freely; with it, Bruce McCandless made the first untethered spacewalk in 1984.

Maragheh Observatory Meraga Rasathanesi

An observatory founded in 1259 under Nasir al-Din al-Tusi with the backing of the Ilkhanid ruler Hulagu, the largest of its age with a great library and staff of scholars.

Mars Mars

The fourth planet from the Sun, reddish because of iron oxide on its surface. It has a thin carbon dioxide atmosphere, giant volcanoes and two small moons, Phobos and Deimos.

Martian dust storm Mars toz fırtınası

A Martian dust storm that can grow from regional scale to engulf the entire planet. A global storm in 2018 ended the mission of the solar-powered Opportunity rover.

Mass ratio Kütle oranı

The ratio of a rocket's fully fuelled mass to its mass once the propellant is used up. The larger the ratio, the more velocity change the rocket equation allows.

Mass transfer Kütle aktarımı

The flow of material in a close binary from a star that fills its Roche lobe onto its companion. It reshapes both stars' evolution and gives rise to novae and X-ray binaries.

Mass–energy equivalence (E = mc²) Kütle-enerji eşdeğerliği (E = mc²)

The principle that mass and energy are interchangeable, with energy equal to mass times the speed of light squared; it explains how stars shine by nuclear fusion.

Mass–luminosity relation Kütle–ışıtma ilişkisi

The relation showing that main-sequence luminosity rises steeply with mass, roughly as mass to the 3.5 power. This is why massive stars burn through their fuel far faster.

Maunder Minimum Maunder Minimumu

The period from about 1645 to 1715 when sunspots were extremely scarce, coinciding with a cold phase of Europe's Little Ice Age.

Max Q Maks Q

The moment of peak dynamic pressure, or aerodynamic load from airspeed, during ascent. It usually comes about a minute after liftoff, and engines are often throttled down through it.

Mayday Mayday

The international distress call, spoken three times on the radio, signalling that an aircraft or its occupants face grave and imminent danger and need immediate help.

Medium Earth orbit (MEO) Orta Dünya yörüngesi

The region between LEO and geostationary orbit, about 2,000–35,786 km. Navigation satellites such as GPS, Galileo and GLONASS fly here at around 20,000 km.

Medium-altitude long-endurance (MALE) Orta irtifa uzun havada kalış (MALE)

A class of unmanned aircraft that flies at medium altitudes and can typically stay aloft for 24 hours or more, designed for persistent reconnaissance and surveillance.

Mega-constellation Mega takımyıldız

A network of hundreds to thousands of satellites in low Earth orbit, usually delivering global broadband internet. Starlink, with thousands of satellites, is the largest example.

Megaparsec (Mpc) Megaparsek

A unit of distance equal to one million parsecs, or about 3.26 million light-years, used for intergalactic distances and in stating the Hubble constant.

Mercury Merkür

The smallest planet and the one closest to the Sun. It has almost no atmosphere, a heavily cratered surface, and completes an orbit in about 88 Earth days.

Merlin engine Merlin motoru

SpaceX's gas-generator engine burning RP-1 and liquid oxygen, used on Falcon 9 and Falcon Heavy. A vacuum version powers the upper stage.

Messier 87 (M87) M87

A giant elliptical galaxy in the Virgo Cluster. In 2019 the Event Horizon Telescope imaged the shadow of its central black hole, about 6.5 billion solar masses.

Messier catalogue Messier kataloğu

A list of nebulae and clusters compiled in the 18th century by French astronomer Charles Messier so they would not be confused with comets. It now has 110 entries; the Andromeda Galaxy is M31.

Metallicity Metalisite

In astronomy every element heavier than hydrogen and helium counts as a metal, and metallicity is their share in a star. Younger stars are more metal-rich, having formed from gas enriched by earlier generations.

METAR METAR

A standard coded weather observation issued at airports, usually every half hour or hour, giving wind, visibility, cloud, temperature and pressure.

Meteor (shooting star) Meteor (akan yıldız)

The brief streak of light seen when a meteoroid enters the atmosphere at high speed and vaporises. Most appear at altitudes of roughly 80–120 km.

Meteor shower Meteor yağmuru

An increase in meteor rates when Earth passes through a stream of debris left along a comet's or asteroid's orbit. Showers recur at about the same dates each year.

Meteorite Göktaşı

A piece of a meteoroid that survives its passage through the atmosphere and reaches the ground. Most come from asteroids, though a few originate on the Moon or Mars.

Meteoroid Meteoroit

A small rocky or metallic fragment travelling through interplanetary space, much smaller than an asteroid. The IAU defines its size as roughly 30 micrometres to 1 metre.

Methalox Metaloks (metan-oksijen)

The propellant pair of liquid methane and liquid oxygen. It burns cleaner than kerosene, easing reuse, and powers the Raptor and BE-4 engines.

Micro Satellite Launch System (MUFS) Mikro Uydu Fırlatma Sistemi (MUFS)

Roketsan's project for a domestic launch system able to place small satellites into low Earth orbit independently. It is part of Türkiye's goal of independent access to space.

Microgravity Mikroçekim

The near-weightless conditions inside an orbiting craft caused by free fall; gravity does not disappear, its effects are simply not felt.

Microwave Mikrodalga

Radiation between infrared and radio waves, with wavelengths of roughly one millimetre to thirty centimetres. The cosmic microwave background is observed in this band.

Milky Way Samanyolu

The barred spiral galaxy that contains the Solar System. It is roughly 100,000 light-years across and is thought to hold 100 to 400 billion stars.

Miller–Urey experiment Miller–Urey deneyi

An experiment published in 1953 that passed electric sparks through a gas mixture mimicking an early atmosphere and showed that amino acids could form without life.

Millisecond pulsar Milisaniye pulsarı

A pulsar with a rotation period of roughly 1–10 milliseconds, thought to have been spun up by accreting matter from a companion. Its extremely regular pulses make it a natural clock.

Mini-Neptune (sub-Neptune) Mini Neptün (alt Neptün)

A planet larger than Earth but smaller than Neptune, thought to have a thick hydrogen-helium or water-rich envelope; among the most common planet types in the galaxy.

Mir Mir

A modular Soviet and later Russian space station that stayed in orbit from 1986 to 2001; aboard it Valeri Polyakov set the record of 437 days in space in a single stay.

Mira variable Mira değişeni

A red giant on the asymptotic giant branch whose brightness swings widely over periods of hundreds of days. It is named after Mira (Omicron Ceti), which has a period of about 332 days.

Mission specialist Görev uzmanı

An astronaut responsible for a mission's scientific and technical work, such as experiments, robotic-arm operations and spacewalks; the role was defined chiefly in the shuttle era.

Mixture ratio (O/F) Karışım oranı

The mass ratio of oxidizer to fuel fed to the engine. It affects performance, temperature and tank sizing; hydrogen-oxygen engines typically run between 5 and 6.

Modified Newtonian dynamics (MOND) MOND (Değiştirilmiş Newton dinamiği)

An alternative to dark matter proposing that gravity behaves differently at very low accelerations. It fits galaxy rotation curves but struggles with clusters and the CMB.

Module Modül

One of the building blocks of a space station, launched separately and joined in orbit, each serving a function such as laboratory, living quarters or connecting node.

Molecular cloud Moleküler bulut

A cold, dense interstellar cloud, about 10–20 K, made mostly of molecular hydrogen. Stars are born in the dense cores within such clouds.

Molniya orbit Molniya yörüngesi

A highly elliptical orbit with a period of about 12 hours and an inclination of 63.4°. The Soviet Union devised it to serve high latitudes that geostationary satellites cover poorly.

Monopropellant Tek bileşenli itken

A propellant that produces hot gas without a separate oxidizer, usually by decomposing over a catalyst. Hydrazine is the most common example in satellite thrusters.

Moon Ay

Earth's only natural satellite, about 3,474 km across and on average some 384,400 km away. It is the only other world humans have walked on.

Moon Agreement Ay Anlaşması

A 1979 UN agreement treating the resources of the Moon and other bodies as the common heritage of mankind; most major spacefaring nations have not joined it.

Multi-layer insulation (MLI) Çok katmanlı yalıtım

A thermal blanket made of many thin, metal-coated plastic sheets separated by gaps. It cuts radiative heat transfer and gives many satellites their gold or silver look.

Multi-messenger astronomy Çok habercili astronomi

The study of a single cosmic event through different messengers, such as light, gravitational waves, neutrinos and cosmic rays. GW170817 is the field's landmark event.

Multispectral imaging Çok bantlı görüntüleme

Recording light in a handful to a few dozen separate visible and infrared bands. Vegetation, water and urban areas are told apart by how differently they reflect in each band.

Multistage rocket Çok kademeli roket

A rocket made of two or more stages, each discarded once its job is done. Most orbital launch vehicles have two or three stages.

Muscle atrophy Kas atrofisi

The weakening and shrinking of muscles freed from supporting the body in microgravity, especially those of the legs and back; regular exercise keeps it in check.

Muwaqqit (timekeeper) Muvakkit

A mosque-attached timekeeper who determined prayer times and the qibla direction with instruments such as the astrolabe, sine quadrant and sundial.

N

Nadir Nadir (ayakucu noktası)

The point on the celestial sphere directly below the observer, opposite the zenith; in satellite work it also means the ground point straight beneath the spacecraft.

Narrowband filter Dar bant filtre

A filter passing only a few nanometres around a specific emission line. Hydrogen-alpha, oxygen-III and sulphur-II filters are common in nebula photography.

NASA Twins Study NASA İkiz Çalışması

A study of how spaceflight affects the body, comparing Scott Kelly during his 340 days on the ISS in 2015–2016 with his identical twin Mark Kelly on Earth.

National Space Program (Türkiye) Milli Uzay Programı

Türkiye's space roadmap announced in February 2021, with ten goals including a lunar mission, a national launch system, a spaceport and flying a Turkish astronaut.

Natural satellite (moon) Doğal uydu

A naturally formed body that orbits a planet, dwarf planet or asteroid under gravity. Earth's Moon, Titan and Phobos are examples.

Near-Earth object (NEO) Dünya'ya yakın cisim

An asteroid or comet whose closest approach to the Sun is less than 1.3 AU, so its orbit can come near Earth's. Tens of thousands are now known.

Near-infrared (NIR) Yakın kızılötesi

The part of the infrared closest to visible light, roughly 0.75 to 2.5 micrometres. Some of it is observable from the ground, and Webb's NIRCam camera works in this range.

Neptune Neptün

The most distant planet from the Sun, discovered in 1846 after its position was calculated from irregularities in Uranus's orbit. It has the fastest winds measured in the Solar System.

Neutral buoyancy pool Nötr yüzerlik havuzu

A large training pool in which astronauts rehearse spacewalks on station mock-ups under conditions that mimic weightlessness; NASA's facility in Houston is a well-known example.

Neutrino Nötrino

An electrically neutral elementary particle with a tiny mass that barely interacts with matter. Vast numbers are made in the Sun, supernovae and active galaxies.

Neutrino oscillation Nötrino salınımı

The change of neutrinos between electron, muon and tau types as they travel. It proves that neutrinos have mass and earned the 2015 Nobel Prize in Physics.

Neutron star Nötron yıldızı

An ultra-dense remnant formed when a massive star's core collapses, about 20 km across yet more massive than the Sun and made mostly of neutrons. A teaspoon of it would weigh billions of tonnes.

New General Catalogue (NGC) Yeni Genel Katalog (NGC)

A deep-sky catalogue published by John Dreyer in 1888, listing about 7,840 nebulae, clusters and galaxies. Together with its Index Catalogue supplements, it remains in wide use.

New Moon Yeni Ay

The phase when the Moon lies between Earth and the Sun, so its sunlit side faces away from us. Solar eclipses can only occur at this phase.

New Shepard New Shepard

Blue Origin's suborbital tourism system, a reusable rocket and capsule that carries six passengers above the Kármán line.

NewSpace Yeni Uzay (NewSpace)

The shift since the 2000s in which private companies have rapidly entered the space sector with low-cost launchers, small satellites and commercial services.

Newton's law of universal gravitation Newton'un evrensel kütleçekim yasası

The law stating that the attraction between two bodies is proportional to the product of their masses and inversely proportional to the square of their separation: F = Gm₁m₂/r².

Newton's laws of motion Newton'un hareket yasaları

Three basic laws covering inertia, force as mass times acceleration (F = ma), and action and reaction; they form the foundation of classical mechanics and orbit calculations.

Newtonian telescope Newton teleskobu

A reflector built by Isaac Newton in 1668, using a concave primary mirror and a flat secondary tilted at 45 degrees. The eyepiece sits on the side of the tube.

Nice model Nice modeli

A model in which the giant planets' orbits shifted after they formed, with Saturn, Uranus and Neptune migrating outward. It aims to explain the structure of the Kuiper belt and Trojan asteroids.

Nitrogen tetroxide (NTO) Azot tetroksit (NTO)

An oxidizer, storable near room temperature, that reacts hypergolically with hydrazine fuels. It is used in spacecraft manoeuvring engines and some launch vehicles.

NOAA space weather scales NOAA uzay havası ölçekleri

A US system that rates geomagnetic storms (G), solar radiation storms (S) and radio blackouts (R) from 1 to 5, describing their likely impacts.

Node module Bağlantı düğümü

A station module that joins other modules together and offers several docking or berthing ports; Unity, Harmony and Tranquility on the ISS are examples.

Normalized difference vegetation index (NDVI) Normalize fark bitki örtüsü indeksi

The difference between near-infrared and red reflectance divided by their sum. It ranges from −1 to +1, with high values indicating dense, healthy vegetation.

Notice to Air Missions (NOTAM) NOTAM

An official notice informing pilots of temporary changes affecting flight safety, such as airspace restrictions, runway closures or navigation-aid outages.

Nova Nova

An explosion caused by the runaway ignition of hydrogen that has built up on a white dwarf's surface from its companion. The system brightens thousands of times, but the white dwarf survives and can erupt again.

Nozzle Lüle (nozul)

The bell- or funnel-shaped part of an engine that expands and accelerates hot gas from the chamber, turning thermal energy into thrust. Rocket nozzles are usually convergent-divergent.

Nuclear fusion Nükleer kaynaşma (füzyon)

The merging of light atomic nuclei into heavier ones, releasing energy. It powers the stars: the Sun converts about 600 million tonnes of hydrogen into helium every second.

Nuclear thermal rocket (NTR) Nükleer termal roket

A rocket in which a nuclear reactor heats a propellant such as hydrogen and expels it through a nozzle. It promises about twice chemical specific impulse; the US tested it in the 1960s under NERVA.

O

Observable universe Gözlenebilir evren

The spherical region from which light has had time to reach us over the age of the universe. Because of expansion, its radius is about 46.5 billion light-years.

Observatory Gözlemevi

A facility housing telescopes and instruments for observing the sky. Sites are chosen high, dry and far from light pollution; Türkiye's Eastern Anatolia Observatory is an example.

Observatory (rasathane) Rasathane

An institution and building for systematic observation of the heavens; the traditional name for observatories in the Ottoman and wider Islamic world.

Occultation Örtme (okültasyon)

The passage of a nearer body in front of a more distant one, hiding it completely; the Moon covering a star or planet is a typical example.

Ocean world Okyanus dünyası

A body such as Europa or Enceladus with a large liquid-water ocean on its surface or beneath an icy shell, making it a prime target in the search for life.

Olbers' paradox Olbers paradoksu

The argument that an infinite, static universe filled with stars would make the night sky bright. The universe's finite age and expansion explain why it is dark.

Olympus Mons Olympus Mons

A giant shield volcano on Mars that rises about 22 km above the surrounding plains, among the tallest known volcanoes in the Solar System. Its base is roughly 600 km wide.

On-board computer (OBC) Yerleşik bilgisayar

The computer aboard a spacecraft that runs flight software, makes autonomous decisions and coordinates subsystems. For reliability it is usually redundant and radiation-tolerant.

One-way light time (OWLT) Tek yönlü ışık süresi

The time a radio signal takes to travel one way between a spacecraft and Earth. For Mars it ranges from about 3 to 22 minutes, so vehicles cannot be steered in real time.

Oort cloud Oort bulutu

A hypothesised spherical shell of icy bodies surrounding the Solar System from thousands to about 100,000 AU out. Thought to supply long-period comets, it has never been observed directly.

Open cluster Açık küme

A loosely bound young group of tens to a few thousand stars born together from the same cloud. They lie in the galactic disk; the Pleiades and Hyades are examples.

Opposition Karşı konum (opozisyon)

The position of an outer planet directly opposite the Sun as seen from Earth; the planet is then visible all night, relatively close and at its brightest.

Optical (laser) communication Optik (lazer) haberleşme

Data transmission using infrared laser light instead of radio. It offers far higher data rates but demands extremely precise pointing and is blocked by clouds.

Orbit Yörünge

The path, closed or open, that a body follows around another body or a common centre of mass under gravity; most orbits are ellipses.

Orbit insertion Yörüngeye giriş manevrası

The engine burn that slows a spacecraft arriving at a target planet so that its gravity captures the craft into orbit, one of a mission's most critical moments.

Orbital elements (Keplerian elements) Yörünge öğeleri (Kepler öğeleri)

The six parameters that define an orbit's shape, orientation and the body's position on it: semi-major axis, eccentricity, inclination, longitude of the ascending node, argument of periapsis and an anomaly.

Orbital inclination Yörünge eğikliği

The angle between an orbital plane and a reference plane such as the ecliptic or Earth's equator; values above 90° indicate a retrograde orbit.

Orbital period Yörünge dönemi

The time a body takes to complete one full orbit; about 365.25 days for Earth and roughly 92 minutes for the International Space Station.

Orbital resonance Yörünge rezonansı

A relationship in which interacting bodies have orbital periods in simple whole-number ratios; Jupiter's moons Io, Europa and Ganymede are in a 1:2:4 resonance.

Orbital slot Yörünge pozisyonu (yörünge yuvası)

A specific longitude assigned to a satellite in geostationary orbit; because they are limited, these slots are a valuable resource coordinated among countries through the ITU.

Orbital velocity Yörünge hızı

The speed of a body along its orbit, equal to √(μ/r) for a circular orbit; in low Earth orbit it is about 7.8 km/s.

Orbiter Yörünge aracı

A spacecraft that enters orbit around a planet, moon or small body to study it over a long period, such as Mars Reconnaissance Orbiter and Cassini.

Orion Nebula (M42) Orion Bulutsusu (M42)

A bright H II region in the sword of Orion, about 1,300 light-years away. It is the nearest large star-forming region to Earth and is visible to the naked eye.

Orion spacecraft Orion

NASA's deep-space capsule for the Artemis programme, designed to carry four astronauts to the Moon and beyond; its service module is supplied by ESA.

Orlan spacesuit Orlan

A semi-rigid Russian spacesuit for spacewalks, which the wearer enters alone through a hatch in the back.

Orthostatic intolerance Ortostatik intolerans

Dizziness or fainting on standing up after landing, because blood pressure cannot be maintained; it results from the cardiovascular system adapting to microgravity.

Outer Space Treaty Dış Uzay Antlaşması

The 1967 treaty declaring space open to all, barring any state from claiming sovereignty over celestial bodies and banning weapons of mass destruction in orbit.

Overview effect Bakış etkisi

The profound shift in thinking and feeling that astronauts describe after seeing Earth whole from space, centred on the planet's fragility and the meaninglessness of borders.

Oxidizer Oksitleyici

The propellant component that supplies oxygen or a similar reactive agent so fuel can burn without air. Liquid oxygen and nitrogen tetroxide are common examples.

Oxygen generation system Oksijen üretim sistemi

Station equipment that splits water into oxygen and hydrogen by electrolysis to provide oxygen for the crew; the hydrogen can be put to use elsewhere.

Pair-instability supernova Çift-kararsızlık süpernovası

A theorized explosion of stars of roughly 130–250 solar masses, triggered when electron–positron pair production saps the core's pressure. It destroys the star completely, leaving no remnant.

Panchromatic image Pankromatik görüntü

A black-and-white image that captures a broad range of visible light in a single band. It offers higher spatial resolution than multispectral bands and is used to sharpen colour imagery.

Panspermia Panspermi

The hypothesis that life, or its building blocks, can be carried between planets or even star systems by meteorites, comets or dust.

Parabolic antenna (dish) Parabolik anten (çanak anten)

A dish-shaped antenna that reflects incoming radio waves onto a feed at its focus. The larger the diameter, the higher its gain and the narrower its beam.

Parabolic flight Parabolik uçuş

A flight in which an aircraft flies parabolic arcs, each giving about 20–25 seconds of weightlessness; it is used for astronaut training and experiments.

Parallax Paralaks

The apparent shift of an object against a distant background when viewed from two different positions; measuring this angle gives the object's distance geometrically.

Parker Solar Probe Parker Güneş Sondası

A NASA spacecraft launched in 2018 that flies through the corona, coming closer to the Sun than any other human-made object to study the solar wind's origins.

Parsec (pc) Parsek (pc)

The distance at which an object shows an annual parallax of one arcsecond, equal to about 3.26 light-years or 206,265 astronomical units.

Payload Faydalı yük

The satellite, spacecraft, cargo or crew a rocket is launched to carry. Launch vehicle capacity is usually stated as the payload mass it can deliver to a given orbit.

Payload fairing Faydalı yük kaplaması (burun konisi)

The shell at the top of a rocket that shields the payload from aerodynamic and heating loads in the atmosphere, split into halves and jettisoned once above it.

Periapsis (periapse) Periapsis (enyakın nokta)

The point in an orbit where the body is closest to the central mass and moves fastest; it is called perigee around Earth and perihelion around the Sun.

Perigee Yerberi (perige)

The point in the orbit of the Moon or a satellite where it is closest to Earth; a full moon near perigee is popularly called a supermoon.

Perihelion Günberi

The point in an orbit around the Sun where a body is closest to the Sun; Earth passes perihelion in early January each year.

Period–luminosity relation (Leavitt law) Dönem–ışıtma ilişkisi (Leavitt yasası)

The relation showing that longer-period Cepheids are more luminous. Discovered by Henrietta Leavitt in 1908–1912, it became a cornerstone of the cosmic distance ladder.

Permanently shadowed region (PSR) Kalıcı gölge bölgesi

Crater floors near the Moon's poles that never receive direct sunlight because the Sun stays so low on the horizon. These extremely cold areas are thought to hold water ice.

Perseids Perseidler

A meteor shower peaking each year in mid-August, usually around 12–13 August. Its parent is Comet 109P/Swift–Tuttle and its radiant lies in Perseus.

Perturbation Pertürbasyon (tedirginlik)

A deviation of a body from its ideal two-body orbit due to effects such as other bodies' gravity, planetary oblateness or atmospheric drag; Neptune was discovered by analysing such deviations.

Phased-array antenna Faz dizili anten

An antenna made of many small elements whose signal phases are adjusted to steer the beam electronically, with no moving parts. Starlink user terminals rely on it.

Phobos and Deimos Phobos ve Deimos

Mars's two small, irregularly shaped moons, discovered by Asaph Hall in 1877. Phobos is slowly spiralling inward and is expected to break apart within tens of millions of years.

Photometry Fotometri

The measurement of the brightness or flux of light from celestial objects. It is usually done through specific filters and expressed in magnitudes or flux units.

Photosphere Fotosfer

The layer a few hundred kilometres thick, at about 5,800 K, that emits most of the Sun's visible light; it is what we see as the Sun's "surface".

Pillars of Creation Yaratılış Sütunları

Column-shaped structures of cold gas and dust in the Eagle Nebula (M16) where stars are still forming. Made famous by Hubble's 1995 image, they have also been imaged by JWST.

Piston engine Pistonlu motor

An internal-combustion engine in which burning fuel-air mixture drives pistons and a crankshaft to turn a propeller; common in light aircraft.

Pitot tube Pitot tüpü

A forward-facing tube that measures total pressure; comparing it with static pressure gives airspeed, and its blockage can lead to serious accidents.

Planck (spacecraft) Planck uydusu

ESA's space observatory that mapped the CMB with high precision from 2009 to 2013. It pinned down the universe's age, composition and Hubble constant.

Planet Gezegen

Under the International Astronomical Union's 2006 definition, a body that orbits the Sun, is massive enough to be pulled into a nearly round shape, and has cleared its orbital neighbourhood.

Planet Nine (hypothetical) Dokuzuncu Gezegen (varsayımsal)

A hypothetical planet several times Earth's mass, proposed in 2016 to explain the clustering of some distant trans-Neptunian orbits. It has not been confirmed by observation.

Planetary defense Gezegen savunması

The detection, tracking, risk assessment and, if needed, deflection of asteroids and comets that could strike Earth.

Planetary differentiation Gezegen katmanlaşması (farklılaşma)

The process by which a young planet or large asteroid melts and its denser materials sink to the centre, separating the interior into core, mantle and crust.

Planetary nebula Gezegenimsi bulutsu

A glowing shell of gas cast off by a low- or intermediate-mass star at the end of its life and lit by the hot core left behind. It has nothing to do with planets; the name comes from its disk-like look in early telescopes.

Planetary protection Gezegen koruma

Principles and practices that keep spacecraft from contaminating other worlds with Earth microbes, and keep returned samples from contaminating Earth with any foreign biological material.

Planetary ring Gezegen halkası

A thin disc of dust, ice and rock particles orbiting in a planet's equatorial plane. All four giant planets have rings, Saturn's being by far the most prominent.

Planetary science Gezegen bilimi

The scientific study of planets, moons, small bodies and the formation of planetary systems, drawing on geology, atmospheric science, physics and chemistry.

Planetesimal Gezegenimsi (planetezimal)

A solid building block, metres to kilometres across, formed as dust and ice clumped together in the disc around the young Sun. Planetesimals collided and merged to build the planets.

Planisphere Planisfer (döner gök haritası)

A star chart made of two rotating discs that, when set to a date and time, shows the sky visible at that moment from a given latitude.

Plate solving Plaka çözme

Software matching the star pattern in a sky image against catalogues to determine exactly where the image points, along with its scale and orientation.

Plate tectonics Levha tektoniği

The division of a planet's outer shell into large moving plates that slide relative to one another. In the Solar System, active plate tectonics is confirmed only on Earth.

Pleiades (M45) Ülker (Pleiades, M45)

A bright open cluster in Taurus, visible to the naked eye, about 440 light-years away and roughly 100 million years old. It is also known as the Seven Sisters.

Pluto Plüton

A Kuiper belt object discovered by Clyde Tombaugh in 1930 and reclassified as a dwarf planet in 2006. NASA's New Horizons flew past it in 2015, mapping its surface in detail.

Pogo oscillation Pogo salınımı

Longitudinal vibration that builds up when thrust fluctuations couple with the propellant feed lines. It caused the early shutdown of the centre engine on Apollo 13's second stage.

Polar alignment Kutup hizalaması

Aiming the rotation axis of an equatorial mount at the celestial pole. In the Northern Hemisphere it points near Polaris, and accuracy is essential for long-exposure photography.

Polar ice cap Kutup buz başlığı

A permanent covering of ice at a planet's poles. Mars's caps are made of water ice, topped each winter by a seasonal layer of frozen carbon dioxide, or dry ice.

Polar orbit Kutupsal yörünge

An orbit inclined close to 90°, carrying the satellite over or near both poles on every revolution. As Earth rotates beneath it, the satellite can eventually view the whole globe.

Polaris (North Star) Kutup Yıldızı (Polaris)

A star in Ursa Minor lying less than a degree from the north celestial pole and long used for navigation. About 430 light-years away, it is a Cepheid variable.

Population I stars Popülasyon I yıldızları

Relatively young, metal-rich stars found mostly in a galaxy's disk and spiral arms. The Sun belongs to this group.

Population II stars Popülasyon II yıldızları

Old, metal-poor stars found mainly in the galactic halo and in globular clusters. They formed early in the history of the universe.

Population III stars Popülasyon III yıldızları

The first stars, formed after the Big Bang from almost pure hydrogen and helium. They are thought to have been very massive and short-lived, and none has yet been observed with certainty.

Potentially hazardous asteroid (PHA) Potansiyel tehlikeli asteroit

An asteroid whose orbit comes within 0.05 astronomical units of Earth's and whose estimated diameter exceeds roughly 140 metres.

Prebreathe Ön nefes alma

Breathing pure oxygen before a spacewalk to flush nitrogen from the blood, reducing the risk of the bends when switching to a low-pressure suit.

Preburner Ön yakıcı

A small combustion chamber in staged-combustion engines that burns part of the propellant to drive the turbopump turbine. Its exhaust is then fed into the main chamber.

Pressure-fed engine Basınç beslemeli motor

A simple engine type in which propellants are pushed into the chamber by high tank pressure, usually from helium, rather than by pumps. It is used mainly in small thrusters and spacecraft.

Pressurized module Basınçlı modül

A module that holds a breathable atmosphere so the crew can work inside without suits; unpressurized sections carry equipment exposed to open space.

Primary mirror Birincil ayna

The main and largest mirror in a reflecting telescope, which collects and focuses incoming light. A telescope's aperture is usually quoted as this mirror's diameter.

Private astronaut mission Özel astronot görevi

A commercial crewed mission organized by a company and paid for by private individuals or countries, travelling to a station such as the ISS; the Axiom missions are examples.

Project Gemini Gemini programı

A NASA programme that flew ten crewed missions in 1965–1966, using two-seat capsules to rehearse lunar techniques such as spacewalks, rendezvous and docking.

Project Mercury Merkür programı

The first US human spaceflight programme, run from 1958 to 1963 with single-seat capsules; Alan Shepard flew suborbitally in 1961 and John Glenn orbited Earth in 1962.

Propellant İtken

The general term for what a rocket consumes to make thrust; in chemical rockets it covers both fuel and oxidizer. Electric thrusters use gases such as xenon as propellant.

Propellant grain Yakıt tanesi (gren)

The shaped block of propellant cast inside a solid motor. The cross-section of its central bore, such as a star shape, sets the burning surface and so the thrust curve over time.

Propeller Pervane

A device turned by an engine whose airfoil-shaped blades push air backwards to create thrust; on variable-pitch propellers the blade angle can be adjusted in flight.

Proper motion Özdevinim (öz hareket)

The slow change of a star's position on the sky over years due to its actual motion through space, usually measured in arcseconds or milliarcseconds per year.

Propulsive landing İtkili iniş

A rocket stage relighting its engines to slow down and land vertically. Falcon 9's first stage first did this on land after an orbital launch in December 2015.

Proton–proton chain Proton–proton zinciri

A series of fusion reactions that turns four protons into a helium-4 nucleus in several steps. It is the main energy source in the Sun and lower-mass stars.

Protostar Ön yıldız (önyıldız)

A young star forming in a collapsing cloud core that is still gathering mass and has not yet begun hydrogen fusion. It shines on gravitational energy released by contraction.

Proxima Centauri Proxima Centauri

A faint red dwarf about 4.24 light-years away, the closest star to the Sun. The planet Proxima b orbits within its habitable zone.

Proxima Centauri b Proxima Centauri b

An exoplanet discovered in 2016 orbiting in the habitable zone of Proxima Centauri, the nearest star to the Sun at about 4.2 light-years.

Pseudorange Sözde uzaklık

The distance a GNSS receiver computes by multiplying a signal's travel time by the speed of light. Because it includes receiver clock error, position and clock offset are solved together using at least four satellites.

Psyche Psyche

An asteroid roughly 220 km across in the main belt, thought to be largely metallic at the surface. NASA's mission of the same name launched in 2023 and should arrive in 2029.

Pulsar Pulsar (atarca)

A rapidly spinning neutron star whose beams of radiation from its magnetic poles sweep past Earth like a lighthouse. The first was discovered in 1967 by Jocelyn Bell Burnell and Antony Hewish.

Pulsar wind nebula Pulsar rüzgârı bulutsusu

A nebula, glowing with synchrotron radiation, blown around a fast-spinning pulsar by its wind of charged particles. The inner Crab Nebula is the best-known example.

Qibla determination Kıble tayini

Finding the direction of the Kaaba in Mecca from a given place, a classic problem in Islamic astronomy solved with spherical trigonometry and instruments like the astrolabe.

Quantum efficiency (QE) Kuantum verimliliği

The percentage of photons striking a detector that are turned into a measurable signal. Scientific CCDs can exceed 90 percent at some wavelengths.

Quasar Kuasar

A very distant, extremely luminous active galactic nucleus that can outshine hundreds of galaxies. The name comes from their first appearance as star-like radio sources.

r-process (rapid neutron capture) r-süreci (hızlı nötron yakalama)

A process in which nuclei capture neutrons too quickly to decay in between. Much of the gold, platinum and uranium in the universe forms this way, notably in neutron star mergers.

Radar Radar

A system that transmits radio waves and receives their echoes to find the range, bearing and speed of targets; used in air traffic control, weather monitoring and defence.

Radial velocity method (Doppler method) Dikine hız yöntemi (Doppler yöntemi)

Finding a planet, and its minimum mass, by measuring the Doppler shift in a star's spectral lines as the planet's gravity tugs the star back and forth.

Radiant Radyant (ışınım noktası)

The point in the sky from which the meteors of a shower appear to fan out. It is a perspective effect, and showers are usually named after the constellation containing it.

Radiation dose Radyasyon dozu

A measure of the biological effect of radiation absorbed by the body, expressed in sieverts (Sv); astronauts on the ISS receive roughly 0.3–0.8 millisieverts a day.

Radiation storm shelter Radyasyon sığınağı

A more heavily shielded part of a spacecraft, protected by water, propellant or equipment, where the crew take refuge during a strong solar particle event.

Radiation-hardened electronics (rad-hard) Radyasyona dayanıklı elektronik

Circuits designed and manufactured to resist damage and errors caused by charged particles and ionising radiation in space. They are slower than commercial chips but far more dependable.

Radiator Radyatör (ısı yayıcı)

A surface that dumps a spacecraft's excess internal heat to space as infrared radiation. With no air to carry heat away, radiation is the main way to shed it.

Radio astronomy Radyo astronomi

The branch of astronomy that studies radio waves emitted by celestial objects. It began when Karl Jansky detected radio emission from the Milky Way in the 1930s.

Radio blackout Radyo kesintisi

A temporary loss of high-frequency (HF) radio communication when X-rays from a solar flare over-ionize the dayside ionosphere.

Radio galaxy Radyo galaksi

A galaxy whose active nucleus drives jets that inflate huge radio lobes far beyond the visible galaxy. Centaurus A and Cygnus A are well-known examples.

Radio telescope Radyo teleskobu

A telescope that collects radio waves from space, usually with a large dish antenna and a sensitive receiver. It can observe in daylight and through cloud.

Radio wave Radyo dalgası

The longest-wavelength part of the electromagnetic spectrum. It passes easily through the atmosphere and carries information about gas clouds, pulsars and galaxies.

Radioisotope thermoelectric generator (RTG) Radyoizotop termoelektrik jeneratör

A power source that turns the decay heat of plutonium-238 into electricity using thermocouples. It powers missions where sunlight is weak or unreliable, such as Voyager, Cassini and Curiosity.

Radiometric resolution Radyometrik çözünürlük

A sensor's ability to distinguish small differences in brightness, expressed in bits. A 12-bit sensor, for example, records 4,096 brightness levels.

Rain fade Yağmur sönümlemesi

Signal weakening caused by raindrops absorbing and scattering radio waves, especially above about 10 GHz. Ku- and Ka-band links need extra power margin to cope with it.

Ramjet Ramjet

A jet engine with no moving parts that compresses air solely through forward speed at the intake; it cannot run from a standstill and is typically efficient between Mach 2 and 5.

Raptor engine Raptor motoru

SpaceX's full-flow staged-combustion engine burning methane and liquid oxygen, developed for Starship. It stands out for its very high chamber pressure.

Reaction control system (RCS) Tepki kontrol sistemi

A set of small thrusters that controls a stage's or spacecraft's orientation and makes small translations. Falcon 9's first stage uses nitrogen gas RCS thrusters on its return.

Reaction wheel Tepki tekerleği

A flywheel spun up or slowed down by an electric motor. By conservation of angular momentum, the spacecraft turns the opposite way, giving precise pointing without using propellant.

Read noise Okuma gürültüsü

Random noise added by the electronics when the charge in a sensor is measured and digitised. It occurs with every readout and limits the detection of faint signals.

Recombination Yeniden birleşme çağı

The era, about 380,000 years after the Big Bang, when the universe cooled enough for electrons to combine with nuclei into neutral atoms, making it transparent to light.

Red dwarf Kırmızı cüce

A cool, faint M-type main-sequence star with about 8 to 50 percent of the Sun's mass. It is the most common type of star in the Milky Way and can live for trillions of years.

Red giant Kırmızı dev

A low- or intermediate-mass star whose outer layers have swelled and cooled to a red color after core hydrogen ran out. The Sun will reach this stage in about 5 billion years.

Red giant branch (RGB) Kırmızı dev kolu (RGB)

The branch of the H–R diagram along which stars with helium cores and hydrogen-burning shells grow brighter and cooler. Helium ignites at the tip of the branch.

Red supergiant Kırmızı süperdev

A cool supergiant whose radius can reach hundreds or even over a thousand times the Sun's. The largest known stars by volume are of this type, such as Betelgeuse and Antares.

Redshift (z) Kırmızıya kayma (z)

The shift of spectral lines to longer wavelengths; z is the change in wavelength divided by the emitted wavelength. It signals recession or cosmic expansion.

Redshift survey Kırmızıya kayma taraması

A sky survey that takes spectra of many galaxies to measure their redshifts and hence their 3D positions. SDSS and DESI are major examples.

Redundancy Yedeklilik

Carrying a second or third copy of critical units so the mission can continue if one fails. Because repairs are rarely possible in space, it is a core design principle.

Reentry blackout Giriş sırasında haberleşme kesintisi

A loss of radio contact lasting several minutes during entry, when the layer of ionized plasma around the vehicle blocks radio signals.

Reflecting telescope (reflector) Aynalı teleskop (reflektör)

A telescope that gathers and focuses light with a curved primary mirror. It is free of chromatic aberration and scales to large sizes, so nearly all research telescopes are reflectors.

Reflection nebula Yansıma bulutsusu

A nebula that produces no light of its own but shines as its dust scatters starlight. Because blue light scatters more, it usually appears blue, as around the Pleiades.

Refracting telescope (refractor) Mercekli teleskop (refraktör)

A telescope that focuses light by bending it through an objective lens at the front. Its sealed tube needs little maintenance; Galileo observed with this type in 1609.

Regenerative cooling Rejeneratif soğutma

A cooling method in which cold or liquid fuel flows through channels in the chamber and nozzle walls, absorbing heat before it is injected and burned.

Regolith Regolit

The layer of loose dust and broken rock covering the surfaces of bodies such as the Moon, Mars and asteroids, ground up by billions of years of impacts.

Relativistic jet Göreli jet

A narrow stream of plasma launched near the speed of light from around a black hole or neutron star. In active galaxies, jets can stretch for millions of light-years.

Relay satellite Röle uydusu

A satellite that forwards data from other spacecraft to the ground. NASA's TDRS satellites and Mars orbiters such as MRO play this role.

Remote sensing Uzaktan algılama

Gathering information about Earth or another body without physical contact, by measuring reflected or emitted electromagnetic radiation. It is widely used in agriculture, disaster management and climate monitoring.

Rendezvous Buluşma

The manoeuvring of two spacecraft until their orbits and speeds match and they are very close together; it is the stage before docking or berthing.

Resolving power (angular resolution) Ayırma gücü (açısal çözünürlük)

The smallest angle at which an optical system can show two close points as separate. Larger apertures and shorter wavelengths allow finer detail to be distinguished.

Retrograde motion Geri hareket (retrograd hareket)

The temporary apparent reversal of a planet's usual eastward drift against the stars, so that it seems to move west; it occurs as Earth overtakes or is overtaken by the planet.

Reusable launch vehicle (RLV) Yeniden kullanılabilir fırlatma aracı

A launch vehicle whose stages, in whole or part, are recovered and flown again. The goal is lower launch costs; Falcon 9 first stages have flown dozens of times.

Revisit time Yeniden ziyaret süresi

The time a satellite or group of satellites needs to image the same spot on Earth again. The two Sentinel-2 satellites together, for instance, revisit the equator about every five days.

Revolution (orbital motion) Dolanma (revolüsyon)

The motion of a body along its orbit around another body; Earth completes one revolution around the Sun in about 365.25 days.

Reynolds number Reynolds sayısı

A dimensionless number giving the ratio of inertial to viscous forces in a flow; it indicates whether flow will be laminar or turbulent and guides the scaling of wind-tunnel tests.

Right ascension (RA) Sağ açıklık

The angular distance measured eastward along the celestial equator from the vernal equinox point, usually expressed in hours, minutes and seconds from 0 to 24 h.

Ritchey–Chrétien telescope Ritchey-Chrétien teleskobu

A Cassegrain variant whose hyperbolic primary and secondary mirrors eliminate coma. The Hubble Space Telescope and many large ground-based telescopes use this design.

Robert Goddard Robert Goddard

The American physicist who pioneered liquid-fuelled rockets. On 16 March 1926, in Massachusetts, he launched the world's first liquid-fuelled rocket, burning gasoline and liquid oxygen.

Roche limit Roche sınırı

The closest distance a self-gravitating moon can approach a primary before tidal forces tear it apart; Saturn's main rings lie largely inside this limit.

Roche lobe Roche lobu

The teardrop-shaped region around each star in a binary within which material stays gravitationally bound to that star. If a star overflows it, matter streams onto its companion.

Rocket Roket

A vehicle that expels high-speed gas from onboard fuel and oxidizer and is pushed forward by the reaction, per Newton's third law. Because it needs no air, it also works in the vacuum of space.

Rocket engine Roket motoru

A machine that produces thrust by burning or energizing propellant and accelerating the resulting gas out of a nozzle. Key parts of a liquid engine are the combustion chamber, injector, turbopump and nozzle.

Rogue planet Başıboş gezegen

A planet roaming the galaxy without being gravitationally bound to any star, probably ejected from its birth system and typically found via microlensing.

Rotation Dönme (rotasyon)

The spinning of a body about its own axis; Earth's rotation produces day and night and the daily rising and setting of celestial objects.

Rover Gezgin (rover)

A robotic vehicle that drives across a body's surface to study different sites, such as NASA's Curiosity and Perseverance rovers on Mars.

RP-1 (rocket-grade kerosene) RP-1 (roket kerosen)

Highly refined kerosene made for rocket engines. It is dense and storable at room temperature; Saturn V's first stage and Falcon 9 burn it with liquid oxygen.

RR Lyrae variable RR Lyrae değişeni

An old, low-mass horizontal-branch star that pulsates with a period under a day. Since they all have nearly the same luminosity, they are used to measure distances to globular clusters.

RS-25 engine RS-25 motoru

A reusable staged-combustion engine burning liquid hydrogen and oxygen, developed for the Space Shuttle. Today four of them power the SLS core stage.

Rudder İstikamet dümeni

A pedal-operated surface hinged to the vertical stabiliser that controls yaw; it is used for crosswind landings and coordinated turns.

Rumi calendar Rumi takvim

A solar calendar based on the Julian calendar but counting years from the Hijra, used in Ottoman financial and official affairs from the 19th century until the 1926 switch to the Gregorian calendar.

Runaway greenhouse effect Kaçak sera etkisi

A feedback loop in which warming releases more greenhouse gases, driving further warming until oceans boil away. Venus is thought to have undergone this process in its past.

Runaway star Kaçak yıldız

A star moving at an unusually high speed, tens of kilometers per second or more relative to its surroundings. It is flung out by a companion's supernova or by close encounters in a cluster.

Runway designation Pist numarası

A two-digit number giving a runway's magnetic heading divided by ten and rounded; a runway pointing 090° is 09, and its opposite end is 27.

Ryugu Ryugu

A carbon-rich near-Earth asteroid about 900 m wide. Japan's Hayabusa2 sampled its surface and subsurface and delivered the material to Earth in 2020.

S band S bandı

The microwave band of roughly 2–4 GHz, widely used for satellite telemetry and command links, some weather radars and spacecraft communications.

s-process (slow neutron capture) s-süreci (yavaş nötron yakalama)

A route to heavy elements in which nuclei capture neutrons slowly enough for radioactive decay to occur between captures. It operates mainly in asymptotic giant branch stars, producing elements such as barium and lead.

S-type asteroid S tipi asteroit

A class of relatively bright, stony asteroids made of silicate minerals with some nickel-iron. Common in the inner asteroid belt; Eros and Itokawa are examples.

Sabatier reactor Sabatier reaktörü

A device that reacts carbon dioxide with hydrogen over a catalyst to make methane and water; it helps close the oxygen loop on the ISS and could produce fuel on Mars.

Safe mode Güvenli mod

A protective state a spacecraft enters when it detects a fault: it halts non-essential activity, points its panels at the Sun and waits for ground commands, buying engineers time.

Sagittarius A* (Sgr A) Sagittarius A

The supermassive black hole at the centre of the Milky Way, with about 4 million solar masses. The Event Horizon Telescope released an image of its shadow in 2022.

Sample return Numune dönüşü

A mission that collects material from a celestial body and brings it back to Earth for study. Hayabusa2 returned samples from Ryugu and OSIRIS-REx from Bennu.

Saros cycle Saros döngüsü

A period of about 18 years, 11 days and 8 hours (6,585.3 days) after which the Sun, Moon and Earth return to nearly the same geometry, so similar eclipses recur.

Satellite bus Uydu platformu

The part of a satellite other than its payload: structure, power, thermal control, attitude control, propulsion and communications. One bus design can be reused across different missions.

Satellite communications (satcom) Uydu haberleşmesi

Relaying voice, data, internet and television signals between distant points via satellites. It provides vital links over oceans, in rural areas and in disaster zones.

Satellite constellation Uydu takımyıldızı

A group of satellites working together on a shared mission, their orbits arranged to complement one another, as in GNSS systems and communications networks.

Satellite galaxy Uydu galaksi

A smaller galaxy bound to and orbiting a larger one. Dozens of satellite galaxies are known around the Milky Way.

Satellite pass Uydu geçişi

The interval during which a satellite is visible to a given ground station, rising above and setting below the horizon. For LEO satellites a pass typically lasts only 5–15 minutes.

Satellite-based augmentation system (SBAS) Uydu tabanlı destekleme sistemi

A system that improves GNSS accuracy by broadcasting corrections and integrity data, computed at ground stations, via geostationary satellites. EGNOS in Europe and WAAS in the US are examples.

Saturn Satürn

The sixth planet from the Sun, famous for its broad ring system of ice and rock particles. It is the only planet whose average density is lower than water's.

Saturn V Satürn V

The three-stage super heavy-lift rocket, over 110 m tall, built for Apollo. It flew 13 times between 1967 and 1973, carried astronauts to the Moon, and had five F-1 engines on its first stage.

Scattered disc Saçılmış disk

A population of icy bodies flung by Neptune's gravity onto highly eccentric, steeply inclined orbits. Eris lives here, and some short-period comets are thought to originate here.

Schmidt–Cassegrain telescope (SCT) Schmidt-Cassegrain teleskobu

A catadioptric telescope with a thin Schmidt corrector plate at the front, a spherical primary and a convex secondary. Its compact design makes it very popular with amateurs.

Schwarzschild radius Schwarzschild yarıçapı

The radius of a non-rotating black hole's event horizon, proportional to its mass. It is about 3 km for one solar mass and about 9 mm for the mass of Earth.

Science of timekeeping (ʿilm al-mīqāt) Mîkat ilmi

The branch of applied astronomy, developed in the Islamic world, that uses spherical astronomy and trigonometry to compute prayer times, the qibla and the calendar.

Scintillation (twinkling) Kırpışma (sintilasyon)

Rapid changes in a star's brightness and colour caused by atmospheric turbulence. Planets show visible discs, so they twinkle much less than stars.

Scramjet (supersonic combustion ramjet) Scramjet

A ramjet in which combustion takes place in air flowing at supersonic speed; designed for hypersonic flight above Mach 5, it took NASA's X-43A to about Mach 9.6 in 2004.

Search for extraterrestrial intelligence (SETI) Dünya dışı zekâ arayışı (SETI)

The umbrella term for scientific efforts to detect radio or optical signals from other civilizations; the first systematic attempt was Project Ozma in 1960.

Segmented mirror Bölümlü ayna

A mirror built from many smaller segments aligned to act as a single large surface. The James Webb telescope's 6.5-metre mirror has 18 hexagonal segments.

Semi-major axis Yarı büyük eksen

Half of the longest diameter of an ellipse; it sets the size of an orbit and, through Kepler's third law, directly determines the orbital period.

Seyfert galaxy Seyfert galaksisi

A galaxy, usually spiral, with a bright active nucleus showing strong emission lines. Less powerful than quasars, it leaves the host galaxy clearly visible.

Shape of the universe Evrenin geometrisi

The large-scale curvature of space: flat, closed (spherical) or open (hyperbolic). CMB measurements show the universe is flat to high precision.

Shenzhou spacecraft Shenzhou

China's three-seat crewed spacecraft; with Shenzhou 5 in 2003, China became the third country to launch a person into space on its own.

Shepherd moon Çoban uydu

A small moon whose gravity confines ring particles and sharpens a ring's edges. Saturn's narrow F ring is herded by Prometheus and Pandora.

Shock wave Şok dalgası

A compression front in supersonic flow across which pressure, temperature and density jump abruptly within a very thin region.

Short-period comet Kısa dönemli kuyruklu yıldız

A comet that orbits the Sun in less than 200 years. Most come from the Kuiper belt and scattered disc, and Jupiter-family comets make up the bulk of them.

Sidereal day Yıldız günü

The time Earth takes to rotate once relative to the distant stars, about 23 hours 56 minutes 4 seconds.

Sidereal time Yıldız zamanı

Time measured relative to the stars; local sidereal time equals the right ascension currently crossing the meridian, which makes it useful for pointing telescopes.

Sidereal tracking Yıldız izleme (takip)

Turning a telescope at the rate needed to cancel Earth's rotation and keep an object in view. That rate is one full turn in about 23 hours 56 minutes.

Sidereal year Yıldız yılı

The time Earth takes to complete one orbit around the Sun relative to the distant stars, about 365.256 days.

Signal-to-noise ratio (SNR) Sinyal-gürültü oranı

The ratio of a measured signal to the random noise mixed into it. Higher values mean more reliable measurements; quadrupling total exposure roughly doubles it.

Simplified Aid for EVA Rescue (SAFER) SAFER

An emergency unit fitted to the spacesuit backpack that lets an astronaut who has come loose during a spacewalk fly back to the station using small nitrogen thrusters.

Sine quadrant Rubu tahtası

A quarter-circle instrument with a grid of sine lines and a plumb thread, used by Ottoman timekeepers for trigonometric calculations and prayer times.

Single-stage-to-orbit (SSTO) Tek kademeyle yörünge (SSTO)

The concept of a vehicle that reaches orbit in one piece without dropping stages. Because the required mass ratio is so high, no vehicle has yet reached orbit this way.

Sirius Sirius (Akyıldız)

The brightest star in the night sky, in Canis Major about 8.6 light-years away. It has a white dwarf companion called Sirius B.

Sky crane Gökyüzü vinci

A landing system in which a rocket-powered descent stage lowers a rover to the surface on cables, then flies off to crash. Curiosity landed this way in 2012 and Perseverance in 2021.

Sky survey Gökyüzü taraması

Systematic imaging and cataloguing of a large part, or all, of the sky. The Sloan Digital Sky Survey and Gaia are well-known examples.

Skylab Skylab

The first US space station, which hosted three crews in 1973–1974 for solar observation and medical research before breaking up on re-entry in 1979.

Slat Slat (hücum kenarı çıtası)

A movable leading-edge surface that extends forward to open a slot, helping the airflow stay attached and raising the stall angle of attack.

Small satellite (smallsat) Küçük uydu

Satellites generally under 500 kg, a class subdivided into mini, micro, nano and pico satellites. Their low cost has driven rapid growth.

SN 1987A SN 1987A

A supernova that exploded in February 1987 in the Large Magellanic Cloud, about 168,000 light-years away. It was the first supernova whose neutrinos were detected, in underground detectors.

Sol Sol (Mars günü)

A solar day on Mars, lasting about 24 hours, 39 minutes and 35 seconds. Missions on the Martian surface keep their schedules in sols.

Solar array Güneş paneli

Deployable wings covered in cells that convert sunlight into electricity. They are the main power source for the vast majority of satellites in Earth orbit.

Solar constant Güneş sabiti

The total solar power falling on a unit area perpendicular to the Sun's rays at Earth's mean distance, outside the atmosphere; about 1,361 W/m², varying only slightly.

Solar core Güneş çekirdeği

The central region of the Sun, at about 15 million K, where hydrogen fuses into helium and generates all of the Sun's energy.

Solar cycle Güneş döngüsü

The roughly 11-year rise and fall of sunspot numbers and solar activity; because the magnetic poles also flip, the full magnetic cycle lasts about 22 years.

Solar day Güneş günü

The interval between two successive meridian crossings of the Sun; its mean value is 24 hours, about four minutes longer than the sidereal day.

Solar energetic particle (SEP) event Güneş enerjik parçacık olayı

An event in which protons accelerated by flares and CMEs reach near-Earth space quickly, posing a radiation hazard to astronauts, satellite electronics and polar flights.

Solar filter Güneş filtresi

A special filter fitted over the front of a telescope that passes only a tiny fraction of sunlight, allowing safe viewing. Looking at the Sun unfiltered causes permanent eye damage.

Solar flare Güneş patlaması (güneş parlaması)

A sudden burst of radiation as magnetic energy is released in the solar atmosphere within minutes; flares are graded A, B, C, M and X by strength.

Solar mass (M☉) Güneş kütlesi (M☉)

A unit equal to the mass of the Sun, about 1.989 × 10³⁰ kg, used to express the masses of stars, black holes and galaxies.

Solar prominence Prominens (güneş fışkırması)

A dense, relatively cool structure of plasma held aloft in the corona by magnetic fields, seen as a bright arch or loop at the Sun's edge.

Solar sail Güneş yelkeni

A method of gaining thrust without propellant by catching the pressure of sunlight on a vast, ultra-thin reflective sheet. Japan's IKAROS demonstrated it in interplanetary space in 2010.

Solar System Güneş Sistemi

The Sun together with everything bound to it by gravity: planets, dwarf planets, moons, asteroids, comets and interplanetary dust. It formed roughly 4.6 billion years ago.

Solar wind Güneş rüzgârı

A continuous outflow of charged particles, mostly protons and electrons, streaming from the corona in all directions at typically 300–800 km/s near Earth.

Solid rocket booster (SRB) Katı yakıtlı güçlendirici

A solid motor strapped to the side of the core stage to add thrust at liftoff, dropped once it burns out. The Space Shuttle and SLS each use two large boosters.

Solid-propellant rocket Katı yakıtlı roket

A rocket whose fuel and oxidizer are premixed and cast as a solid block inside the casing. It is simple, storable and powerful, but usually cannot be shut off once lit.

Solstice Gündönümü

The moment the Sun reaches its farthest point north or south of the celestial equator, giving the longest day around 21 June and the shortest around 21 December in the northern hemisphere.

Sonic boom Sonik patlama

The thunder-like noise heard when shock waves from an object flying supersonically reach the ground; it has led many countries to restrict civil supersonic flight over land.

Sound barrier Ses duvarı

The sharp rise in drag and control problems near the speed of sound; it was first officially broken by Chuck Yeager in the Bell X-1 on 14 October 1947.

Sounding rocket Sonda roketi

A research rocket that climbs into the upper atmosphere or space and falls back without entering orbit. It is used for a few minutes of microgravity and high-altitude measurements.

South Atlantic Anomaly Güney Atlantik Anomalisi

An area over South America and the South Atlantic where the magnetic field is weak and the inner Van Allen belt dips closest to Earth, causing glitches in low-orbit satellites.

South Pole–Aitken basin Güney Kutbu–Aitken havzası

A huge impact basin on the Moon's far side, about 2,500 km across. It is one of the largest and oldest known impact structures in the Solar System.

Soyuz rocket Soyuz roketi

A Russian launcher from the R-7 family, flying since 1966. It is recognizable by its four strap-on boosters and carries crewed Soyuz spacecraft to orbit.

Soyuz spacecraft Soyuz

A three-seat Russian crewed spacecraft in service since 1967; its descent module lands on the Kazakh steppe under parachute, with braking rockets fired just before touchdown.

Space adaptation syndrome Uzay adaptasyon sendromu

Nausea, dizziness and vomiting in the first days of flight, caused by balance signals from the inner ear clashing with vision; it usually passes within a few days.

Space debris (orbital debris) Uzay çöpü (yörünge enkazı)

Defunct satellites, spent rocket stages and fragments from collisions or explosions left in orbit; at orbital speeds even tiny pieces are dangerous.

Space economy Uzay ekonomisi

All economic activity linked to space, such as launch, satellite manufacturing, communications, Earth observation and navigation services, and the value they create.

Space farming Uzayda bitki yetiştirme

Growing plants aboard a spacecraft with controlled light, water and nutrients; in 2015 astronauts ate lettuce grown in the Veggie unit on the ISS.

Space food Uzay yemeği

Specially packaged food designed to keep for long periods, meet nutritional needs and be eaten without scattering crumbs or droplets in microgravity.

Space habitat Uzay habitatı

A pressurized, shielded structure that lets people live for long periods in space or on the surface of another world.

Space Launch System (SLS) Uzay Fırlatma Sistemi (SLS)

NASA's super heavy-lift rocket for the Artemis programme. Its core stage has four RS-25 engines plus two solid rocket boosters; it first flew on Artemis I in November 2022.

Space law Uzay hukuku

The body of national and international law governing activities in space, built on five international treaties drafted under the United Nations.

Space medicine Uzay hekimliği

The branch of medicine that studies how the space environment affects human health and looks after astronauts' selection, in-flight care and recovery after landing.

Space mining Uzay madenciliği

The extraction and use of water ice, metals and other resources from asteroids, the Moon or other bodies; its legal framework is still debated.

Space probe Uzay sondası

An uncrewed spacecraft that travels beyond Earth orbit to study planets, moons, small bodies or interplanetary space. Voyager 1 and 2 are the best-known examples.

Space radiation Uzay radyasyonu

Ionizing radiation that astronauts face in space, made up of galactic cosmic rays, solar particle events and trapped belt radiation; it raises the risk of cancer and tissue damage.

Space Shuttle Uzay Mekiği

NASA's partly reusable launch and return system that flew 135 missions from 1981 to 2011. It consisted of an orbiter, an external tank and two solid rocket boosters.

Space situational awareness (SSA) Uzay durumsal farkındalığı (SSA)

Knowing the positions, motion and potential hazards of satellites, debris and natural threats in orbit by tracking them with radar and telescopes.

Space station Uzay istasyonu

A large orbiting structure built for people to live and work in for weeks or months, with crew and supplies brought up by other vehicles.

Space sustainability Uzay sürdürülebilirliği

Principles and practices that protect the orbital environment from debris, congestion and collision risk so space stays usable for future generations.

Space telescope Uzay teleskobu

A telescope placed in orbit or deep space to escape the blurring and absorption of Earth's atmosphere. Hubble, James Webb and Chandra are well-known examples.

Space tourism Uzay turizmi

Paying private individuals travelling to space for leisure or personal reasons; Dennis Tito became the first paying tourist when he visited the ISS in 2001.

Space weather Uzay havası

The changing conditions in near-Earth space driven by solar activity, which can disrupt satellites, communications, navigation systems and power grids.

Spacecraft cemetery (Point Nemo) Uzay aracı mezarlığı (Nemo Noktası)

The area around the point in the South Pacific farthest from land, where spacecraft are deliberately brought down; the Mir station ended there.

Spaceflight participant Uzay uçuşu katılımcısı

The official term for someone who is not a professional astronaut but joins a spaceflight under a private arrangement; it includes space tourists.

Spaceflight-associated neuro-ocular syndrome (SANS) Uzay uçuşuyla ilişkili nöro-oküler sendrom

Flattening of the eyeball, swelling of the optic disc and vision changes seen in some astronauts on long flights; it is thought to be linked to the fluid shift.

Spaceport Uzay limanı

A site where rockets are prepared, launched and sometimes landed, with pads, assembly buildings, propellant plants and control centres. Locations with open sea to the east or south are preferred.

SpaceShipTwo SpaceShipTwo

Virgin Galactic's class of tourist spaceplane, released in mid-air from a carrier aircraft, rocketing into suborbital space and gliding back to a runway.

Spacesuit Uzay giysisi

A personal protective system that shields an astronaut from vacuum, temperature extremes, radiation and micrometeoroids while supplying pressure, oxygen and cooling.

Spacetime Uzay-zaman

The combination of three dimensions of space and one of time into a single four-dimensional continuum; in general relativity, mass and energy curve it.

Spacewalk Uzay yürüyüşü

An astronaut leaving the spacecraft in a spacesuit to work in open space; Alexei Leonov made the first one on 18 March 1965.

Spaghettification Spagettileşme

The stretching of an object falling toward a black hole into a long, thin shape because gravity pulls much harder on its near end than its far end. It is an extreme example of tidal forces.

Spatial resolution Uzamsal çözünürlük

The size of the smallest ground detail that can be distinguished in an image. At 50 cm a car is visible; at 30 m only individual fields can be told apart.

Special relativity Özel görelilik

Einstein's 1905 theory, built on the laws of physics being the same for all inertial observers and the constancy of the speed of light; it predicts time dilation and length contraction.

Specific impulse (Isp) Özgül itki

A measure of how efficiently an engine uses propellant, expressed in seconds as how long a unit weight of propellant can deliver a unit of thrust. Hydrogen-oxygen engines reach about 450 s in vacuum.

Spectral line Tayf çizgisi

A narrow bright or dark feature at a specific wavelength in a spectrum. It arises from transitions between energy levels in atoms or molecules and acts like an element's fingerprint.

Spectral resolution Tayfsal çözünürlük

A spectrograph's ability to distinguish two nearby wavelengths. It is usually given as R, the wavelength divided by the smallest separable difference.

Spectral type (spectral class) Tayf sınıfı (spektral tip)

A classification of stars by the absorption lines in their spectra, which reflect surface temperature. From hottest to coolest the classes are O, B, A, F, G, K and M; the Sun is G2.

Spectrograph Tayfçeker (spektrograf)

An instrument that splits light from a telescope into its wavelengths with a grating or prism and records the resulting spectrum on a detector.

Spectroscopic binary Tayfsal çift

A star system whose components cannot be seen separately but whose binary nature shows up as periodic Doppler shifts in its spectral lines.

Spectroscopy Tayfölçüm (spektroskopi)

The study of light spread out into its wavelengths. It reveals an object's chemical make-up, temperature, density and radial velocity.

Spectrum allocation Frekans tahsisi

The division of radio frequency bands among satellite, terrestrial and other services, managed through ITU regulations and national licences to prevent interference.

Speed of light (c) Işık hızı (c)

The speed of light and all electromagnetic waves in a vacuum, exactly 299,792,458 metres per second; it is the upper limit for transmitting information.

Sphere of influence (SOI) Etki küresi

The approximate region around a planet within which its gravity, rather than the Sun's, is treated as dominant for a body's motion; for Earth its radius is about 925,000 km.

Spherical aberration Küresel sapma

Blurring that occurs when rays through the edge and the centre of a spherical lens or mirror focus at different points. Hubble's original mirror flaw was of this kind.

SPICE SPICE

An information system and software toolkit from NASA's NAIF group that stores and computes spacecraft position, orientation and the geometry of celestial bodies.

Spin Vril (spin)

A self-sustaining condition in which one wing is more deeply stalled than the other, so the aircraft descends steeply while rotating in a tight spiral.

Spin stabilization Dönüşle kararlılık

Keeping a spacecraft's orientation by spinning it about an axis so gyroscopic stiffness resists disturbances. Simple and robust, it was used by early satellites and probes such as Juno.

Spiral arm Sarmal kol

A curved structure winding outwards through the disk of a spiral galaxy, outlined by young bright stars and gas clouds. The Sun lies in the Milky Way's Orion Arm.

Spiral galaxy Sarmal galaksi

A galaxy made of a central bulge and a flat, rotating disk whose spiral arms are sites of ongoing star formation. Andromeda and the Milky Way are examples.

Splashdown Okyanusa iniş

The landing of a capsule in the sea after slowing under parachutes, after which a waiting recovery ship lifts the capsule and crew from the water and brings them ashore.

Spoiler Spoyler

A panel that rises from the upper wing surface to disrupt the airflow, cutting lift and adding drag; it acts as a ground brake on landing and aids descent and roll control.

Spot beam Nokta hüzme

A narrow beam that concentrates a satellite's power on a limited area. It lets the same frequencies be reused in different beams, multiplying capacity.

Squawk code Squawk kodu

The four-digit transponder code assigned to an aircraft by ATC; 7500 signals unlawful interference, 7600 radio failure and 7700 a general emergency.

Stage Kademe

A section of a rocket with its own engines and tanks that is dropped when its propellant runs out. Shedding empty tanks is what lets a rocket reach orbit.

Stage separation Kademe ayrılması

The release of a spent stage from the stage above it using pyrotechnic, pneumatic or mechanical systems. The upper-stage engine fires once separation is complete.

Staged combustion cycle Kademeli yanma çevrimi

An engine cycle in which preburner gas that drives the turbine is routed into the main chamber instead of being dumped. It is highly efficient; RS-25 and RD-180 use it.

Stall Tutunma kaybı (perdövites)

A sudden loss of lift when the angle of attack exceeds its critical value and the airflow separates from the upper wing surface; it can occur at any airspeed.

Stall speed Tutunma kaybı hızı

The lowest speed at which an aircraft can maintain level flight for a given weight and configuration; it drops with flaps extended and rises with weight and bank angle.

Standard candle Standart mum

An astronomical object of known intrinsic brightness whose distance can be found by comparing it with its apparent brightness. Cepheids and Type Ia supernovae are the best known.

Standard gravitational parameter (μ) Standart kütleçekim parametresi (μ)

The product of a body's mass and the gravitational constant (μ = GM), known more precisely than the mass itself; for Earth it is about 398,600 km³/s².

Star Yıldız

A hot sphere of plasma held together by its own gravity that shines by nuclear fusion in its core. The Sun is the star closest to Earth.

Star catalogue Yıldız kataloğu

A compilation listing stars' positions, brightnesses and other properties. Its history runs from Hipparchus to Gaia's catalogue of more than a billion stars.

Star chart Gök haritası (yıldız haritası)

A map showing the positions of stars, constellations and other celestial objects. It helps observers find their targets.

Star formation Yıldız oluşumu

The process by which interstellar gas and dust collapse under gravity and condense into new stars. It usually begins in molecular clouds and passes through a protostar phase.

Star hopping Yıldızdan yıldıza atlama

Finding a faint target by moving step by step from bright, easy stars using a chart. It is the basic technique for observers without motorised mounts.

Star tracker Yıldız izleyici

A camera that images the sky and matches star patterns against an onboard catalogue to determine orientation to within arcseconds. It is among the most accurate attitude sensors.

Starburst galaxy Yıldız patlaması galaksisi

A galaxy forming stars at an exceptionally high rate, often triggered by a merger or close encounter. The Cigar Galaxy (M82) is a classic example.

Starlink Starlink

SpaceX's broadband internet network of thousands of satellites in low Earth orbit. The satellites are linked by lasers, and users connect through phased-array terminals.

Starship Starship

SpaceX's super heavy-lift system, made up of the Super Heavy booster and the Starship upper stage and designed to be fully reusable. Both stages use methalox Raptor engines.

Static fire test Statik ateşleme testi

A test in which engines are fired briefly while the rocket or engine is held down, to verify its systems. It is often done a few days before launch.

Station-keeping İstasyon tutma

Keeping a satellite at its assigned orbital position with small thruster burns that counter perturbations such as gravitational irregularities and solar radiation pressure. In GEO it largely sets fuel lifetime.

Stellar evolution Yıldız evrimi

The sequence of changes a star undergoes from birth to death. Its course is set mainly by initial mass: low-mass stars end as white dwarfs, massive ones as neutron stars or black holes.

Stellar nucleosynthesis Yıldız nükleosentezi

The creation of new chemical elements inside stars and in their explosions. Elements up to iron form through core fusion, while heavier ones come mostly from neutron-capture processes.

Stellar parallax (annual parallax) Yıldız paralaksı (yıllık paralaks)

The small apparent shift of a nearby star over a year caused by Earth's orbit around the Sun; a star with a parallax of one arcsecond lies one parsec away.

Stellar wind Yıldız rüzgârı

A continuous outflow of gas and charged particles from a star's upper atmosphere. In hot massive stars and red giants it is strong enough to strip away much of the star's mass.

Stellar-mass black hole Yıldız kütleli kara delik

A black hole of a few to several tens of solar masses formed by the collapse of a massive star's core. They are detected through X-ray binaries and gravitational waves.

Subgiant Altdev

A star that has just run out of core hydrogen and is leaving the main sequence on its way to becoming a giant. It is assigned luminosity class IV.

Suborbital flight Yörünge altı uçuş

A flight that reaches space but, lacking orbital velocity, returns to Earth without completing an orbit. New Shepard tourist flights and sounding rockets are examples.

Subsurface ocean Yüzey altı okyanusu

A layer of liquid water beneath the icy crust of a moon or dwarf planet. Europa, Enceladus, Ganymede and Titan are thought to have them, making them key targets in the search for life.

Sun sensor Güneş algılayıcı

A simple, reliable sensor that measures the direction of the Sun relative to the spacecraft, used especially to point the solar panels sunward in safe mode.

Sun-synchronous orbit (SSO) Güneş eşzamanlı yörünge

A near-polar orbit, inclined about 98°, whose plane swings round once a year. The satellite passes over any given area at the same local solar time each day, ideal for imaging.

Sundial Güneş saati (mizvele)

A device that tells solar time from the position of a rod's or edge's shadow; Ottoman mosques often carried them on their walls to mark prayer times.

Sunspot Güneş lekesi

A region on the Sun's surface where intense magnetic fields suppress heat flow, making it roughly 1,500–2,000 K cooler than its surroundings and therefore dark.

Super heavy-lift launch vehicle Süper ağır yük roketi

A launch vehicle class able to lift more than 50 tonnes to low Earth orbit. Saturn V, SLS and Starship are examples.

Super-Earth Süper Dünya

A class of exoplanet more massive than Earth but well below Uranus and Neptune; no such planet exists in our Solar System.

Supercluster Üstküme

A large structure made of galaxy groups and clusters, spanning hundreds of millions of light-years. As a whole it is not gravitationally bound.

Supergiant Süperdev (üstdev)

A very large, luminous star with tens of solar masses and tens to hundreds of thousands of times the Sun's luminosity. Its luminosity class is I, and most end as supernovae.

Supermassive black hole Süper kütleli kara delik

A black hole of millions to billions of solar masses found at the center of large galaxies. M87* was imaged in 2019, and Sgr A* at the Milky Way's center in 2022.

Supermoon Süper Ay

A full moon that coincides with the Moon being near its closest point to Earth. It looks about 14% larger and 30% brighter than a full moon at its farthest point.

Supernova Süpernova

A colossal stellar explosion at the end of a star's life, briefly bright enough to outshine an entire galaxy. It scatters heavy elements into space.

Supernova remnant Süpernova kalıntısı

The expanding shell of gas formed as material blasted out by a supernova plows into the interstellar medium. It can stay visible for tens of thousands of years; the Crab Nebula and Cassiopeia A are examples.

Supersonic flight Süpersonik uçuş

Flight faster than the speed of sound, above Mach 1, which generates shock waves and sonic booms.

Survival training Hayatta kalma eğitimi

Training that prepares astronauts to endure and be rescued if their capsule comes down somewhere unplanned, such as at sea, in forest or on snowy ground.

Sustainable aviation fuel (SAF) Sürdürülebilir havacılık yakıtı

Fuel made from waste oils, biomass or synthetic processes that can be blended with fossil jet fuel, aiming to cut life-cycle carbon emissions substantially.

Swath width Tarama genişliği

The width of the strip of ground a satellite sensor images in one pass. Sentinel-2's swath, for example, is about 290 km wide.

Swept wing Ok açılı kanat

A wing angled backwards (or occasionally forwards) from root to tip; common on jets because it delays shock-wave formation near the speed of sound.

Synchrotron radiation Sinkrotron ışınımı

Radiation emitted by near-light-speed electrons spiralling in magnetic fields. It produces much of the light from jets, radio galaxies and supernova remnants.

Synodic month Kavuşum ayı (sinodik ay)

The average time for the Moon to return to the same phase, for example from new moon to new moon; about 29.53 days, it underpins lunar calendars.

Synodic period Kavuşum dönemi (sinodik dönem)

The time a body takes to return to the same position relative to the Sun as seen from Earth, such as between successive oppositions; for Mars it is about 780 days.

Synthetic aperture radar (SAR) Sentetik açıklıklı radar

An imaging radar that uses the satellite's motion to make a small antenna act like a very large virtual one. Sending its own microwave pulses, it sees through cloud and works at night.

T

T Tauri star T Tauri yıldızı

A pre-main-sequence variable star of roughly solar mass, typically only a few million years old. It shows irregular brightness changes, strong winds and a surrounding disk of gas and dust.

Taikonaut Taykonot

An informal name for astronauts of China's human spaceflight programme; the first, Yang Liwei, flew on Shenzhou 5 in 2003.

Tail rotor Kuyruk rotoru

A small vertical rotor at the tail that counters the torque from the main rotor and provides pedal-controlled yaw.

Takeoff decision speed (V1) Kalkış karar hızı (V1)

The highest speed during the take-off run at which the take-off can still be rejected; beyond it the take-off continues even if an engine fails.

Tank pressurization Tank basınçlandırma

Keeping propellant tanks under pressure during flight to ensure steady flow to the pumps and to stiffen the structure. Helium or heated propellant gas is usually used.

Taqi al-Din Takiyüddin

A 16th-century Ottoman astronomer and engineer who founded the Istanbul Observatory and is noted for using mechanical clocks in his observations.

Technosignature Teknoişaret

An observable trace, such as radio transmissions, laser pulses or industrial pollutants, that could point to another civilization's technology.

Telemetry Telemetri

The remote measurement of a spacecraft's temperatures, voltages, position and status, sent down to the ground. Operators monitor the vehicle's health with these data.

Telemetry, tracking and command (TT&C) Telemetri, izleme ve komuta

The combined functions of receiving a spacecraft's status data, measuring its position and velocity, and sending it commands, covering both onboard and ground equipment.

Telescope Teleskop (ırakgörür)

An instrument that collects and focuses light or other electromagnetic radiation with lenses or mirrors, making distant objects appear brighter and more detailed.

Temporal resolution Zamansal çözünürlük

How often the same area can be imaged. Geostationary weather satellites revisit within minutes, while polar-orbiting observation satellites take days.

Terrestrial planet Karasal gezegen (kayaç gezegen)

A relatively small, dense planet made of rock and metal with a solid surface. In the Solar System, Mercury, Venus, Earth and Mars belong to this group.

Thermal control subsystem (TCS) Isıl kontrol alt sistemi

The subsystem that keeps spacecraft components within allowable temperatures, balancing differences of hundreds of degrees between sunlit and shaded sides with insulation, coatings, radiators and heaters.

Thermal protection system (TPS) Isıl koruma sistemi

All the materials and structures that protect a vehicle from extreme heating during entry or ascent. Ablative shields, ceramic tiles and insulating blankets are all part of it.

Thermal protection tile Isı karosu

Silica- or ceramic-based tiles of very low heat conductivity that cover reusable vehicles. The Space Shuttle carried thousands of them, and Starship uses hexagonal tiles.

Three-axis stabilization Üç eksenli stabilizasyon

Holding a spacecraft in a fixed orientation by actively controlling it about all three axes. Most modern communication and observation satellites work this way.

Three-body problem Üç cisim problemi

The problem of determining the motion of three bodies interacting through gravity; in general it has no closed-form solution and the motion can be chaotic.

Throttling Kısma (itki ayarı)

An engine's ability to raise or lower thrust by changing propellant flow. It is used to ease loads around Max Q and to touch down gently in propulsive landings.

Thrust İtki

The reaction force an engine exerts on the vehicle as it expels exhaust. It is measured in newtons or kilonewtons; Falcon 9's first stage produces about 7.6 MN at sea level.

Thrust reverser Ters itki

A mechanism that redirects engine exhaust or fan air forwards after touchdown to help slow the aircraft, reducing wear on brakes and tyres.

Thrust vector control (TVC) İtki vektör kontrolü

Steering a rocket by changing the direction of engine thrust. It can be done by gimbaling the engine, injecting fluid into the nozzle or using a movable nozzle.

Thrust-to-weight ratio (TWR) İtki/ağırlık oranı

The ratio of the thrust an engine or vehicle produces to its own weight. A rocket can only lift off the pad if this ratio exceeds 1 at launch.

Tiangong space station Tiangong

China's modular space station in low Earth orbit; its core module Tianhe was launched in 2021 and it usually hosts three taikonauts.

Tidal disruption event (TDE) Gelgit bozulması olayı (TDE)

The shredding of a star by tidal forces when it strays too close to a supermassive black hole. As part of the debris falls in, a bright flare lasting months is observed.

Tidal force Gelgit kuvveti

The stretching effect produced by differences in gravitational pull across a body; Earth's ocean tides are caused mainly by the Moon.

Tidal heating Gelgit ısınması

Internal heat generated by friction as a moon is repeatedly flexed by its planet's changing gravity along an eccentric orbit. It powers Io's volcanoes and keeps Europa's ocean liquid.

Tidal locking (synchronous rotation) Gelgit kilitlenmesi

The state in which tidal friction has made a body's rotation period equal its orbital period; this is why the Moon always shows the same face to Earth.

Tiltrotor Tiltrotor (dönebilir rotorlu uçak)

An aircraft whose wingtip rotors tilt upwards for vertical take-off and forwards for cruise, combining helicopter and aeroplane traits; the V-22 Osprey is a well-known example.

Time dilation Zaman genişlemesi

The slowing of a clock that is moving relative to an observer or sits deeper in a gravitational field; it has been measured in particle accelerators and satellites.

Timekeeper's house (muvakkithane) Muvakkithane

A small building, usually in an Ottoman mosque courtyard, where the timekeeper determined prayer times and set the clocks.

Titan Titan

Saturn's largest moon and the only moon with a thick atmosphere, made mostly of nitrogen. Lakes of liquid methane and ethane dot its surface; the Huygens probe landed there in 2005.

Tolman–Oppenheimer–Volkoff limit (TOV limit) Tolman–Oppenheimer–Volkoff limiti (TOV limiti)

The maximum mass a neutron star can reach without collapsing, estimated at about 2–3 solar masses. Beyond it, collapse produces a black hole.

Torino scale Torino ölçeği

A 0-to-10 scale that communicates impact risk to the public by combining an object's probability of hitting Earth with the energy of the impact.

Traffic collision avoidance system (TCAS) TCAS

A system that interrogates nearby aircraft transponders to assess collision risk, issuing a traffic advisory and, if needed, a climb or descend resolution advisory to the pilot.

Trans-Neptunian object (TNO) Neptün ötesi cisim

Any minor body orbiting the Sun at a greater average distance than Neptune, beyond about 30 AU. Kuiper belt and scattered disc objects belong to this group.

Transit (astronomical) Geçiş (transit)

The passage of a small-looking body across the disc of a larger one, such as Mercury or Venus crossing the face of the Sun.

Transit method Geçiş yöntemi (transit yöntemi)

Detecting a planet, and gauging its size, from the small, regular dip in starlight as it passes in front of its star.

Transit of Venus Venüs geçişi

The passage of Venus directly between Earth and the Sun, appearing as a small dark dot on the solar disc. It occurs in pairs more than a century apart; the last two were in 2004 and 2012.

Transiting Exoplanet Survey Satellite (TESS) TESS (Geçiş Yapan Ötegezegen Tarama Uydusu)

A NASA satellite launched in 2018 that scans nearly the whole sky for transiting planets around nearby, bright stars.

Transmission spectroscopy İletim tayfı (geçiş tayfölçümü)

Analysing starlight filtered through a planet's atmosphere during a transit to identify molecules such as water vapour and carbon dioxide.

Transponder Transponder (aktarıcı)

The receive-and-transmit chain on a communications satellite that picks up a signal from the ground, shifts its frequency, amplifies it and sends it back down. A satellite may carry dozens.

TRAPPIST-1 system TRAPPIST-1 sistemi

A system of seven Earth-sized planets orbiting a cool red dwarf about 40 light-years away, several of them within the habitable zone.

Triple-alpha process Üçlü alfa süreci

The reaction in which three helium-4 nuclei fuse into carbon-12 at around 100 million kelvin. It drives helium burning in the cores of red giants.

Triton Triton

Neptune's largest moon, which orbits backwards relative to the planet's rotation, suggesting it is a captured Kuiper belt object. Voyager 2 saw nitrogen plumes on its surface.

Trojan asteroids Truva asteroitleri

Asteroids sharing a planet's orbit and clustered around the L4 and L5 Lagrange points, 60° ahead of or behind it. Jupiter's are the largest group and are the target of the Lucy mission.

Tropical year Dönencel yıl (tropik yıl)

The time between successive vernal equinoxes, about 365.2422 days; it is the basis of calendars that keep in step with the seasons.

True airspeed (TAS) Gerçek hava hızı

An aircraft's actual speed relative to the surrounding air mass; it becomes increasingly higher than indicated airspeed with altitude as air density falls.

True anomaly Gerçek anomali

The angle, measured at the central body, between periapsis and the orbiting object's current position; it gives where the body actually is at a given moment.

Tsiolkovsky rocket equation Tsiolkovski roket denklemi

The fundamental equation giving a rocket's change in velocity as exhaust velocity times the natural log of initial to final mass: Δv = vₑ·ln(m₀/m_f). Tsiolkovsky published it in 1903.

Tunguska event Tunguska olayı

The 30 June 1908 airburst of an asteroid or comet fragment over Siberia. It left no crater but flattened roughly 2,000 km² of forest.

Turbofan Turbofan

A jet engine with a large front fan that sends part of the air around the core; quieter and more fuel-efficient, it powers most of today's airliners.

Turbojet Turbojet

An early type of gas-turbine engine that gets all of its thrust from the exhaust of air passed through its compressor, combustor and turbine; efficient at high speed but noisy.

Turboprop Turboprop

An engine in which a gas turbine drives a propeller through a reduction gearbox; it is very fuel-efficient at moderate speeds and on short regional routes.

Turbopump Turbopompa

A pump assembly driven by a turbine that forces propellants from the tanks into the chamber at very high pressure. It is what makes high thrust possible in large liquid engines.

Turkish Astronaut and Science Mission Türk Astronot ve Bilim Misyonu

Türkiye's first human spaceflight effort; Alper Gezeravcı flew to the ISS on Ax-3 in January 2024 and Tuva Cihangir Atasever made a suborbital flight in June 2024.

Turkish Space Agency (TUA) Türkiye Uzay Ajansı (TUA)

The government agency established by presidential decree in December 2018 to set Türkiye's space policy and run its National Space Program.

Türksat 6A Türksat 6A

Türkiye's first communications satellite designed and built domestically. It was launched on a Falcon 9 in July 2024 and entered service in geostationary orbit.

Twilight Alacakaranlık

The period when the Sun is below the horizon but scattered sunlight still lights the sky; it is classed as civil (0–6° below), nautical (6–12°) and astronomical twilight (12–18°).

Two-body problem İki cisim problemi

The problem of the motion of two point masses attracting only each other; it has an exact analytical solution, giving orbits shaped as conic sections.

Type Ia supernova Tip Ia süpernova

A supernova from the thermonuclear explosion of a white dwarf, with no hydrogen lines in its spectrum. Its fairly uniform peak brightness makes it a standard candle, and it led to the discovery of dark energy.

Type II supernova Tip II süpernova

A core-collapse supernova of a massive star whose spectrum shows hydrogen lines, meaning the star still had its outer hydrogen envelope.

UBV photometric system UBV fotometrik sistemi

A system for measuring stellar brightness through three standard filters: ultraviolet (U), blue (B) and visual (V). Defined by Johnson and Morgan in the 1950s, it was later extended to red and infrared bands.

Ultra-high-energy cosmic ray (UHECR) Ultra yüksek enerjili kozmik ışın

A cosmic ray with energy above 10¹⁸ electronvolts. Its sources remain uncertain; the 1991 "Oh-My-God" particle carried about 3×10²⁰ eV.

Ultraviolet (UV) Morötesi

Radiation with wavelengths shorter than visible violet light and longer than X-rays. Largely absorbed by atmospheric ozone, it is observed from space and reveals hot young stars.

Ulugh Beg Uluğ Bey

A 15th-century Timurid ruler and astronomer who founded the Samarkand observatory and gave star positions with high accuracy in the zij that bears his name.

Ulugh Beg Observatory Uluğ Bey Rasathanesi

The observatory built in Samarkand in the 1420s by the Timurid ruler and astronomer Ulugh Beg, famed for its giant marble meridian arc and a catalogue of over 1,000 stars.

Unified model of AGN Birleşik AGN modeli

The model holding that quasars, Seyferts, blazars and other AGN types are the same basic object, their differences arising mostly from viewing angle relative to an obscuring dusty torus.

Unmanned aerial vehicle (UAV) İnsansız hava aracı (İHA)

An aircraft with no pilot on board that flies by remote control or autonomously on pre-programmed missions, used for reconnaissance, mapping, delivery and more.

Uplink Yukarı bağlantı

The radio link from a ground station up to a satellite or spacecraft, used to send commands and content to be relayed.

Upper stage Üst kademe

The stage that carries the payload to its target orbit after the lower stage drops away, usually designed to work in vacuum. Centaur and Falcon 9's second stage are examples.

Uranus Uranüs

The seventh planet from the Sun. Its spin axis is tilted about 98°, so it rotates almost on its side. William Herschel discovered it with a telescope in 1781.

V

V-2 rocket V-2 roketi

A ballistic missile developed by Germany in World War II, burning ethyl alcohol and liquid oxygen. In 1944 it became the first human-made object to reach space and laid the groundwork for postwar rocketry.

Valles Marineris Valles Marineris

A vast canyon system running about 4,000 km along Mars's equator and reaching depths of around 7 km. It is named after the Mariner 9 spacecraft that imaged it.

Van Allen radiation belts Van Allen kuşakları

Two zones, inner and outer, of energetic charged particles trapped by Earth's magnetic field, discovered in 1958 from Explorer 1 data.

Variable star Değişen yıldız

A star whose brightness changes over time. The variation can come from the star itself, through pulsation or outbursts, or from external causes such as eclipses by a companion.

Venus Venüs

The second planet from the Sun. Its thick carbon dioxide atmosphere keeps the surface near 465 °C, and it spins very slowly in the opposite direction to most planets.

Vernal equinox point (First Point of Aries) İlkbahar noktası (koç noktası)

The point where the Sun crosses the celestial equator from south to north along the ecliptic; it serves as the zero point of right ascension and ecliptic longitude.

Very small aperture terminal (VSAT) Çok küçük açıklıklı terminal

A two-way satellite ground terminal with a dish usually under 1–3 metres. It provides data links for banks, fuel stations, ships and remote work sites.

Very-long-baseline interferometry (VLBI) Çok uzun taban çizgisi interferometrisi (VLBI)

Interferometry combining atomic-clock-timed recordings from radio telescopes continents apart. The Event Horizon Telescope used it to image black holes.

Vesta Vesta

The second most massive body in the asteroid belt, a differentiated protoplanet remnant. Dawn orbited it in 2011–2012, and it is thought to be the source of HED meteorites.

VHF omnidirectional range (VOR) VOR

A ground-based radio navigation aid transmitting in the 108–117.95 MHz band that lets an aircraft determine its magnetic bearing from the station.

Virgo Cluster Başak Kümesi

The nearest large galaxy cluster, about 54 million light-years away and containing more than a thousand galaxies. It lies at the heart of the Local Supercluster.

Vis-viva equation Vis-viva denklemi

The equation relating an orbiting body's speed to its distance from the central mass and the orbit's semi-major axis, v² = μ(2/r − 1/a); it follows from conservation of energy.

Visible light Görünür ışık

Electromagnetic radiation the human eye can detect, with wavelengths of roughly 380 to 750 nanometres. It spans the colours from violet to red.

Visual binary Görsel çift

A binary whose components can be seen separately through a telescope, so their orbital motion can be followed directly. If the distance is known, the orbit yields the total mass.

Visual flight rules (VFR) Görerek uçuş kuralları

Rules under which the pilot navigates and avoids other aircraft by looking outside, permitted only when visibility and cloud clearance meet set minimums.

Vostok 1 Vostok 1

The Soviet spacecraft that made history's first crewed spaceflight, carrying Yuri Gagarin on a single orbit lasting about 108 minutes on 12 April 1961.

Vostok programme Vostok programı

The first Soviet human spaceflight programme, which made six single-seat flights between 1961 and 1963; on Vostok 6 in 1963 Valentina Tereshkova became the first woman in space.

Wake turbulence İz türbülansı

Turbulence left behind aircraft, especially heavy ones, by their wingtip vortices; time and distance spacing is applied between aircraft on take-off and landing because of it.

Waste management system Atık yönetim sistemi

A space toilet that collects body waste with airflow in microgravity; on the ISS, urine is processed and fed into water recovery.

Water recovery system Su geri kazanım sistemi

A system that purifies urine, sweat and cabin humidity back into drinking water; on the ISS about 98 percent of water can be recovered.

Wave drag Dalga sürüklemesi

Extra drag caused by shock waves forming as an aircraft approaches and exceeds the speed of sound; swept wings and the area rule are used to reduce it.

Wavelength Dalga boyu

The distance between successive crests of a wave. For electromagnetic radiation, shorter wavelengths mean higher frequency and more energetic photons.

Weak gravitational lensing Zayıf merceklenme

Tiny distortions in the shapes of distant galaxies caused by foreground mass, too small to see individually but measurable statistically. It is used to map dark matter.

Weakly interacting massive particle (WIMP) WIMP

A hypothetical heavy particle interacting only through gravity and the weak force, proposed to explain dark matter. Underground detectors are searching for it, so far without success.

Weather satellite Meteoroloji uydusu

A satellite that tracks clouds, temperature, humidity and storms to feed weather forecasts and climate research. Geostationary and polar-orbiting types complement each other.

Weightlessness Ağırlıksızlık

The loss of any feeling of weight because a body and everything around it are falling freely together; astronauts in orbit are continually falling around Earth.

Wet dress rehearsal (WDR) Islak prova

A full rehearsal in which the rocket is loaded with real propellants on the pad and the countdown is run up to just before ignition. SLS went through several before Artemis I.

White dwarf Beyaz cüce

The hot core left after a Sun-like star sheds its outer layers: about Earth-sized yet close to a solar mass, made mostly of carbon and oxygen. It slowly cools over time.

Wind shear Rüzgâr kesmesi

A sudden change in wind speed or direction over a short distance; it is especially dangerous during take-off and landing, when it can abruptly cut airspeed.

Wing loading Kanat yüklemesi

An aircraft's weight divided by its wing area; low values allow slower take-offs and landings, while high values give a smoother ride at high speed.

Winglet Winglet (kanat ucu çıkıntısı)

A small upturned surface at the wingtip that weakens tip vortices, reducing induced drag and saving fuel.

Wingtip vortex Kanat ucu girdabı

A rotating tube of air formed as high-pressure air beneath the wing curls around the tip to the upper surface; it causes induced drag and wake turbulence for following aircraft.

Wolf–Rayet star Wolf–Rayet yıldızı

A very hot, massive evolved star that has lost its outer hydrogen layers to powerful winds. Its spectrum shows broad emission lines of helium, nitrogen or carbon.

Wolter telescope Wolter teleskobu

A design that focuses X-rays by letting them strike mirrors at very shallow grazing angles. X-ray observatories such as Chandra and XMM-Newton use nested mirrors of this kind.

Wow! signal Wow! sinyali

A strong narrowband radio signal lasting about 72 seconds, recorded by Ohio's Big Ear telescope on 15 August 1977; its source was never identified and it was never detected again.

Wright Flyer Wright Flyer

The aircraft in which the Wright brothers made the first powered, controlled, sustained heavier-than-air flight at Kitty Hawk on 17 December 1903; the first hop lasted 12 seconds.

X

X band X bandı

The microwave band of roughly 8–12 GHz, used for deep-space communications, military satcom, radar and downloading Earth-observation data.

X-ray X-ışını

High-energy radiation with wavelengths shorter than ultraviolet and longer than gamma rays. In space it comes from gas at millions of degrees and black hole surroundings, and the atmosphere absorbs it.

X-ray astronomy X-ışını astronomisi

The branch of astronomy that studies X-ray emission from celestial objects. Because X-rays cannot penetrate the atmosphere, observations are made from rockets and satellites.

X-ray binary X-ışını çifti

A binary in which a neutron star or black hole pulls matter from its companion and emits X-rays. They are divided into low-mass and high-mass systems according to the companion's mass.

Y

Yellow dwarf Sarı cüce

The common name for a G-type main-sequence star. The Sun is one and will spend about 10 billion years on the main sequence; its true color is close to white.

Zarya Zarya

The first module of the International Space Station, launched in November 1998; a Russian-built functional cargo block that initially provided power, storage and propulsion.

Zenith Zenit (başucu noktası)

The point on the celestial sphere directly above the observer, opposite the direction of gravity, at an altitude of 90°.

Zenithal hourly rate (ZHR) Saatlik zenit oranı

The number of meteors a single observer would see in an hour with the radiant overhead under ideal dark skies showing stars to magnitude 6.5. It is used to compare showers.

Zij Zîc

In Islamic astronomy, a handbook of tables and rules for computing the positions of the Sun, Moon and planets; the Zij of Ulugh Beg is among the most famous.

Zodiac Burç kuşağı (zodyak)

The band of sky on either side of the ecliptic within which the Sun, Moon and planets appear to move; it is traditionally divided into twelve signs.

See the terms in action on Satellite science and the Rocket engine atlas.

Sources and method

Turkish equivalents follow the Turkish Language Association (TDK), TÜBA Turkish Science Terms and Turkish Astronomical Society usage.
Definitions written by SpaceTRC to be consistent with NASA, ESA, IAU and textbook definitions.

Last updated: 2 November 2026

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