A distance taken as a convenient unit of length. Within the Solar System the unit distance is the astronomical unit (au), the average distance of the Earth from the Sun. For stellar distances the light year (l.y.) or the parsec (pc) is used. Larger units such as the kiloparsec (1000 pc) or the megaparsec (1 000 000 pc) are used for distances within our Galaxy or to other galaxies.