Spark image
Astronomical distances

Astronomical unit
One Astronomical unit (AU) is the mean distance of the Earth from the Sun (1.5x1011 m)

The light year
This is the distance that light travels in free space in one year = 9.5x1015m

The Parsec
This is the distance at which an object subtends an angle of one second using the radius of the Earth’s orbit as the baseline.
1 Parsec = 3.06x1016 m = 2.04x105 AU = 3.26 light years
1 Megaparsec = 3.26x106 light years = 3.097x1022 m

© Keith Gibbs 2007