Absolute magnitude is the measure of
intrinsic brightness of a celestial object. It is the hypothetical
apparent magnitude of an object at a standard
distance of exactly 10
parsecs (32.6
light years) from the
observer, assuming no
astronomical extinction of starlight. This places the objects on a common basis and allows the true energy output of astronomical objects to be compared without the distortion introduced by distance. As with all astronomical
magnitudes, the absolute magnitude can be specified for different wavelength intervals; for stars the most commonly quoted absolute magnitude is the
absolute visual magnitude, which uses only the visual (V) band of the spectrum (
UBV system). Also commonly used is the
absolute bolometric magnitude, which is the total
luminosity expressed in magnitude units that takes into account energy radiated at all wavelengths, whether visible or not.