| Units in astronomy | Kilometres | Miles | Astronmomical units |
| Astronomical unit (a.u.)- distance Earth to Sun | 1.496 X 108 | 9.296 X 107 | |
| Light-year (l.y.) | 9.461 X 1012 | 5.879 X 1012 | 63 X 103 |
| Parsec (pc) | 30.857 X 1012 | 19.174 X 1012 | 206 X 103 |
| Kiloparsec (kpc) = 103 parsecs | |||
| Megaparsec (mpc) = 106 parsec | |||
| Velocity of light in a vaccum = 2.998 X 105 km per second (km/s) |