Astronomical Distance Converter
Convert between kilometers, miles, astronomical units, light-years, and parsecs.
How these units are defined
An astronomical unit (AU) is the average distance from Earth to the Sun — a natural yardstick for distances within our solar system. A light-year is the distance light travels in one Julian year, used for distances between stars. A parsec, used mainly by astronomers, is defined from parallax angle measurements and is the largest of the three.
Common conversions
- 1 AU ≈ 149.6 million km — roughly the Earth-Sun distance
- 1 light-year ≈ 9.46 trillion km ≈ 63,241 AU
- 1 parsec ≈ 3.26 light-years ≈ 30.86 trillion km
- The nearest star system to our Sun, Alpha Centauri, is about 4.24 light-years away
Frequently asked questions
Why do astronomers use parsecs instead of light-years?
A parsec comes directly from how astronomers actually measure stellar distances — via parallax, the apparent shift in a star's position as Earth orbits the Sun — making it a more natural unit for their measurement method, even though light-years are more intuitive for general audiences.
Is a light-year a unit of time or distance?
Distance, despite containing the word 'year'. It's the distance light travels in one year, used as a convenient distance unit precisely because interstellar distances are so vast that kilometers become an unwieldy number of digits.