Parsec
This is the most commonly used measurement in space used by astronomers. One parsec is 3.26 light years and is used when for any distance even for very large ones, which in that case we put a prefix in front. This measurement is expressed by (pc).

Kilo parsec and mega parsec
A kilo parsec is 1000 parsecs and it is shown by (kpc). A mega parsec is a million parsecs and shown by (mpc).

Kilometers
This measurement is commonly used on Earth, but can be used in space as well. It is not frequently used by astronomers but is used every now and then.

Astronomical Units
This unit is the distance between the earth and sun. This measurement is expressed by (AU).