Absolute magnitude

Absolute magnitude is the apparent magnitude an astronomical object would have if viewed from 10 parsecs away, expressing its intrinsic brightness on the logarithmic magnitude scale.

Distance modulus: The difference between an object's apparent magnitude and absolute magnitude, determined by its distance. It converts measured apparent magnitude into absolute magnitude when distance is known.
Astronomical magnitude: A logarithmic system for expressing the brightness of celestial objects. Absolute magnitude is one form of this brightness system.
Hertzsprung–Russell diagram: A plot relating stars' luminosities or absolute magnitudes to their surface temperatures or colors. Absolute magnitude places stars vertically on widely used versions of this diagram.
Apparent magnitude: A logarithmic measure of an astronomical object's brightness as observed from Earth or another specified location. Unlike absolute magnitude, it describes observed brightness without standardizing distance.
Parsec: A unit of astronomical distance equal to about 3.26 light-years. The standard distance in the definition is exactly 10 parsecs.
Pogson's ratio: The brightness ratio of 100 to 1 assigned to a difference of five astronomical magnitudes. This ratio makes absolute magnitude logarithmic rather than a linear brightness measure.
Main sequence: The band on a Hertzsprung–Russell diagram occupied by stars fusing hydrogen in their cores. Main-sequence stars are classified and compared using their absolute magnitudes.
Visual magnitude: An astronomical magnitude measured in or approximating the visible-light range. It restricts brightness to visible wavelengths, whereas absolute magnitude can be defined in other bands.
Inverse-square law: A law stating that radiation intensity from a point source decreases in proportion to the square of distance. Its distance dependence explains why brightness must be corrected before comparing intrinsic luminosities.
Bolometric magnitude: An object's magnitude calculated from its total emitted energy across all wavelengths. It is the absolute-magnitude form that accounts for radiation beyond a single band.

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