UnitSnapAstronomical Distance converter
Astronomical distances are so large that ordinary units become unwieldy. The astronomical unit (au), roughly the average Earth-Sun distance, was fixed by the International Astronomical Union in 2012 at exactly 149,597,870,700 meters. It is the natural unit for distances within the solar system.
Convert between 6 astronomical distance units. Pick any two units below; results update as you type.
Popular astronomical distance conversions
About astronomical distance units
The light-second, exactly 299,792,458 m, is the distance light travels in one second. The light-year is the distance light travels in one Julian year of 365.25 days, about 9.46 trillion kilometers. Professional astronomers usually prefer the parsec, about 3.26 light-years, for distances to stars and galaxies.
The parsec comes from parallax: it is the distance at which one astronomical unit subtends an angle of one arcsecond. Kiloparsecs and megaparsecs describe galactic and intergalactic scales.
Tips
- A light-year is a distance, not a unit of time, despite its name.
- Sunlight takes roughly 8.3 minutes to reach Earth, so the Earth-Sun distance is roughly 500 light-seconds.
- For very large values, use scientific notation to avoid miscounting zeros.
All astronomical distance units
| Unit | Symbol | Value in kilometers |
|---|---|---|
| Kilometers | km | 1 km = 1 km |
| Miles | mi | 1 mi = 1.609344 km |
| Light-Seconds | ls | 1 ls = 299,792.5 km |
| Light-Years | ly | 1 ly = 9,460,730,000,000 km |
| Astronomical Units | au | 1 au = 149,597,900 km |
| Parsecs | pc | 1 pc = 30,856,780,000,000 km |
Convert offline on your phone. 36 categories, live currency rates, calculators and history in our free Unit Converter app.
Factors: NIST SP 811 · SI Brochure · NIST Handbook 44 — Updated