One of the ways of measuring distance to stars is to use the astronomical parallax. The apparent shift in position of a star as it orbits the sun. The reciprocal of this measured in seconds of arc is the distance in Parsecs. The largest parallax is about 3/4 of a second of arc or a distance of 1.3 parsecs. So no star is within a parsec and most parallaxes are far smaller than this or the stars are much further away. Using 10 parsecs is thus a compromise and big enough to include all stars except the sun.
Hope this helps.
St. Mary's University
From: Phys-l [mailto:firstname.lastname@example.org] On Behalf Of Bill Nettles
Sent: Friday, September 14, 2012 3:09 PM
Subject: [Phys-L] absolute magnitude
I've done some searching, but obviously not in the right places:
How did astronomers arrive at 10 parsecs as the distance used for computing absolute magnitudes?