Apparent magnitude is a measure of the observed brightness of a celestial object. Apparent magnitude depends on an objects actual (intrinsic) brightness, its distance from the observer, and, in the case of objects outside the Solar System, the amount of absorption by intervening matter. The brighter an object appears, the smaller the numerical value of its apparent magnitude. A star that is one magnitude brighter than another (e.g., +1 versus +2) looks 2.5 times brighter.
Among the brightest objects in the sky are the Sun (apparent magnitude -26.7), the full Moon (-12.6), Venus (at brightest, -4.7), Sirius (-1.44), Canopus (-0.62), Alpha Centauri (-0.27), and Arcturus (-0.05). On a clear, dark night, the unaided eye can see stars as faint as apparent magnitude +6.
Unless otherwise qualified, the term is normally taken to mean apparent visual magnitude.
Integrated magnitude is the apparent magnitude that an extended object, such as a nebula or galaxy, would have if all its light were concentrated at a starlike point.