SPACETRC / ATOM TO COSMOS
One universe.
Extraordinary scales.
From an atomic reference length to the Milky Way: explore the gap with numbers. Change the scale, compare two lengths and calculate how long light would take to cross the same distance.
01 / CHANGE THE SCALE
One step, ten times the span.
A whole unit on the slider changes the length by a factor of ten. Decimal positions let you examine the scales between them.
Equal distances on this axis mean equal factors. The dots do not depict object sizes.
Earth diameter
Approximate mean diameter; Earth is not a perfect sphere.
- Light-crossing time
- Ratio to Earth diameter
02 / COMPARE
Think in ratios.
Comparing an aircraft length with Earth’s diameter makes the scale difference tangible. Check the diameter, radius and distance labels: this compares lengths, not mass or volume.
03 / OPEN THE MODEL
Striking numbers. Transparent assumptions.
Why logarithmic?
A linear ruler cannot meaningfully fit an aircraft and a galaxy on one screen. Here p = log₁₀(L / 1 m). Moving from 2 to 3 means moving from 100 metres to 1,000 metres. The nearest reference is chosen by logarithmic distance; the slider’s actual length is shown separately.
What does light-crossing time mean?
We use t = L / c with c = 299,792,458 m/s. This is a one-way crossing of the selected length in stationary vacuum. It does not model propagation through an object, gravitation, cosmic expansion or spacecraft travel. At atomic scales the result is simply a length-to-speed ratio.
Which quantities are exact?
The speed of light and astronomical unit are defined quantities. The nominal solar diameter is a conversion reference derived from the defined IAU B3 nominal solar radius. Our light-year uses 365.25 × 86,400 seconds. The Bohr radius has experimental uncertainty; displayed digits support this educational comparison. Earth and galaxy sizes are rounded. The human, cell and aircraft values are explicitly chosen examples.
Reference notebook
Every value remains readable without the interactive view. Unit conversions and ratios use these stated quantities.
| Reference | Length | Context |
|---|---|---|
| Bohr radius | 0.0529177 nm | Atomic unit of length; not a hard atomic surface or a diameter. Source ↗ |
| Example cell scale | 10 µm | A chosen 10 µm example length; cells do not all have this size. |
| Example human height | 1.7 m | A height selected for this activity, not a population average. |
| Example aircraft length | 60 m | A 60 m educational example, not a specification for a particular aircraft. |
| Earth diameter | 12,742 km | Approximate mean diameter; Earth is not a perfect sphere. Source ↗ |
| Earth–Moon distance | 384,400 km | Average orbital separation between centres, not a diameter. Source ↗ |
| Nominal solar diameter | 1,391,400 km | Twice the IAU B3 nominal solar radius; not an instantaneous physical diameter measurement. Source ↗ |
| Astronomical unit | 149,597,870,700 m | A defined length unit, not the instantaneous Earth–Sun separation. Source ↗ |
| One light-year | 9.46073 × 10¹⁵ m | Distance light travels in vacuum in a Julian year of 365.25 days; not a unit of time. Source ↗ |
| Milky Way stellar disc | ≈ 100,000 light-years | About 100,000 light-years across; a galaxy has no single sharp boundary. Source ↗ |
TRACEABLE REFERENCES
Check the quantities.
- NIST · CODATA 2022 / Bohr radius ↗
- NASA JPL · Earth–Moon model ↗
- NASA · Earth and Moon ↗
- IAU · Resolution B3 (2015), nominal solar radius ↗
- IAU · Measuring the Universe ↗
- NASA · Milky Way scale ↗
- NIST · Speed of light in vacuum ↗
Editorial check: 24 October 2026. Values are selected references, not a complete physical catalogue. Illustrations are original SpaceTRC diagrams.