The measurement often used to express the brightness of stars is called magnitude. There are two types of magnitude: apparent magnitude, which measures how bright a star appears from Earth, and absolute magnitude, which reflects the star's brightness at a standard distance of 10 parsecs. The scale is logarithmic: a decrease of 1 in magnitude is associated with an increase in brightness by about 2.5 times. Astronomers use this system to compare the luminosity of different stars and understand stellar evolution.