COSMOS / CONSTELLATIONS / HYA
Hydra (Water Snake)
The Water Snake. IAU abbreviation Hya. One of the 48 classical constellations listed by Ptolemy in the Almagest in the 2nd century AD.
STAR CHART
KEY FACTS
- IAU abbreviation
- Hya
- Latin name / genitive
- Hydra / Hydrae
- Position
- Right ascension ≈ 10 h 33 m; declination −36° to +6°
- Visibility from Türkiye
- Visible in full from anywhere in Türkiye. When it crosses the meridian its centre stands about 35° above the horizon from Ankara.
- Best time to observe
- Best placed at 21:00 Türkiye time around 27 April.
- Number of stars
- 245 stars brighter than magnitude 6.5 in the catalogue; 44 brighter than 5 and 12 brighter than 4.
INTERACTIVE LAB
Where is Hydra tonight?
The lab opens for Ankara on today’s date. Drag the time slider through the night; the “Best night” button jumps to the date when the constellation is highest at 21:00 (around 27 April). Change the city to compare the view from elsewhere in Türkiye and around the world.
MYTH, HISTORY AND OBSERVING
The many-headed water snake slain by Heracles; it is the largest of the 88 constellations, stretching more than 100 degrees across the sky. Its brightest star, Alphard, means “the solitary one” in Arabic, as it has no bright neighbours. The Southern Pinwheel Galaxy (M83) is here.
BRIGHTEST STARS
| Star | Magnitude | Distance (light-years) | Spectral type |
|---|---|---|---|
| Alphard | 1.99 | 180 | K3III |
| γ Hya | 2.99 | 134 | G8III |
| ζ Hya | 3.11 | 167 | G8III-IV |
| ν Hya | 3.11 | 144 | K0/K1III |
| π Hya | 3.25 | 101 | K2III |
| Ashlesha | 3.38 | 129 | G0III-IV |
| ξ Hya | 3.54 | 130 | G8III |
| λ Hya | 3.61 | 113 | K0III |
Magnitude: apparent brightness; the smaller the number, the brighter the star. Distances derive from parallax measurements and are uncertain for distant stars. Source: HYG v4.1 star catalogue (CC BY-SA 4.0).
SOURCES
Position, visibility and best observing time were computed approximately for this page from the catalogue stars (Ankara, 39.9° N). The 88 constellations were adopted by the IAU in 1922; their boundaries were drawn by Eugène Delporte in 1930.