What are the advantages of using the Parsec over the lightyear?
If two equidistant light sources 1 AU apart reveal angular spacing of
Light year is light-speed-oriented unit of distance. Parsec is a distance unit that has other advantages.
Parsec measure is quite useful to study dimensions of galaxies clusters that are thousands/millions of light years away.
Average Earth-Sun distance = 1 AU = 149597871 km
The formula used for evaluating parsec is
the length of circular arc subtending
L = R
1 parsec is defined as 1/ (angular spacing 1" in radian) AU.
Thus, 1 parsec
= 206264.8 AU
Note that the linear spacing in-between very far equidistant objects is approximately the circular arc length, when the angular spacing is quite small.