Apparent magnitude is a measure of how bright a star appears in the night sky. It is based on the amount of light that reaches Earth from the star, and takes into account the star's distance from Earth and any interstellar absorption that may occur. The apparent magnitude scale is logarithmic, meaning that each whole number difference in magnitude corresponds to a difference in brightness of about 2.5 times.

The brightest star in the night sky, Sirius, has an apparent magnitude of -1.46, while the faintest stars visible to the naked eye have apparent magnitudes of about +6. The apparent magnitude of the Sun is -26.74.

Apparent magnitude is different from absolute magnitude, which is a measure of how bright a star would appear if it were placed at a standard distance of 10 parsecs (32.6 light-years) from Earth. Absolute magnitude takes into account the star's intrinsic luminosity and is not affected by the star's distance from Earth.