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Space-scale distances, times and masses made easy to picture. Convert light-years, astronomical units and parsecs, see how long light takes to reach us from the Sun or a star, and find out what you would weigh on Mars.
| Unit | Equal to | Typically used for |
|---|---|---|
| Astronomical unit (AU) | 149,597,870.7 km (exact) | Distances within the solar system |
| Light-year (ly) | 9.461 trillion km, or 63,241 AU | Distances to stars and galaxies in popular science |
| Parsec (pc) | 3.2616 ly, or 206,265 AU | Professional astronomy |
| Speed of light (c) | 299,792.458 km/s (exact) | Light travel time |
| Solar mass (M☉) | 1.989 × 10³⁰ kg | Star and black hole masses |
| Sidereal day | 23 h 56 min 4.09 s | Telescope tracking, star time |
| Body | Gravity vs Earth | A 150 lb person weighs |
|---|---|---|
| Moon | 0.166 | 25 lb |
| Mercury | 0.38 | 57 lb |
| Venus | 0.91 | 136 lb |
| Mars | 0.38 | 57 lb |
| Jupiter | 2.53 | 380 lb |
| Saturn | 1.07 | 160 lb |
| Uranus | 0.89 | 133 lb |
| Neptune | 1.14 | 171 lb |
Distance. A light-year is how far light travels in one Julian year: about 9.461 trillion kilometers or 5.879 trillion miles.
About 3.26 light-years. A parsec is the distance at which a star shows a parallax of one arcsecond, so distance in parsecs = 1 ÷ parallax in arcseconds.
About 499 seconds, or 8 minutes 19 seconds, at the average Earth–Sun distance of 1 AU.
Earth moves along its orbit as it spins, so it must turn about 1° extra each day to bring the Sun back overhead. A sidereal day (one turn relative to the stars) is about 3 minutes 56 seconds shorter than the 24-hour solar day.