Distances

Typical units for distance used in Astronomy:

1 AU = Astronomical Unit = average Earth-Sun distance
1 AU = 1.495979 x 10¹¹ m = 1.495979 x 10⁸ km.

1 ly = Light Year = distance traveled by light in one year
1 ly = 9.46053 x 10¹⁵ m = 9.46053 x 10¹² km = 0.30659486 pc.

1 pc = Parsec = distance at which a star has parallax angle of 1 arc-second. ( 206265 is the number of arc-seconds in one radian of angular measure.)
1 pc = 206265 AU = 3.085678 x 10¹⁶ m = 3.085678 x 10¹³ km = 3.261633 ly.

Of course, then we can multiply any these by one thousand or one million or one billion to get bigger units: kpc, Mpc, and Gpc, for example.