Magnitude

Magnitude, measure of a celestial object's brightness. The foundations of the system were laid by Hipparchus (120 B.C.), who divided stars into 6 categories of relative brightness, as seen from the earth (apparent magnitude). On a logarithmic scale, the difference of 1 magnitude of brightness between objects is determined by a factor of 2,512 (the 5th root of 100). The sun's magnitude is 26.8; bright stars, about +1. Absolute magnitude (measure of intrinsic brightness) is defined as the apparent magnitude if located at a distance of 10 parsecs.

See also: Astronomy; Hipparchus.