How do astronomers determine whether to use astronomical units, light years or parsecs?

1 Answer
A. S. Adikesavan
Mar 1, 2016

The smallest AU used for in-between distances of orbiters in a star system, like solar system. A much larger ly is used for stellar distances, Parsec is a little larger.

Explanation:

Parsec has an advantage over ly. It is related to angular spacing across for seemingly single but really globular groups of stars. Mega parsec used for distances of far distant galaxies.
1 AU = 149597870 km
1 ly = 63242 AU, nearly.
1 parsec = 206265 AU nearly.

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