Editing Absolute magnitude (section)

{{Short description|Measure of the luminosity of celestial objects}}
{{About|the brightness of stars|the science fiction magazine|Absolute Magnitude (magazine)}}
{{Use dmy dates|date=April 2020}}

In [[astronomy]], '''absolute magnitude''' ('''{{mvar|M}}''') is a measure of the [[luminosity]] of a [[celestial object]] on an inverse [[Logarithmic scale|logarithmic]] [[Magnitude (astronomy)|astronomical magnitude]] scale; the more luminous (intrinsically bright) an object, the lower its magnitude number. An object's absolute magnitude is defined to be equal to the [[apparent magnitude]] that the object would have if it were viewed from a distance of exactly {{convert|10|pc|ly|1|abbr=off|lk=on}}, without [[Extinction (astronomy)|extinction]] (or dimming) of its light due to absorption by [[Interstellar medium|interstellar matter]] and [[cosmic dust]]. By hypothetically placing all objects at a standard reference distance from the observer, their luminosities can be directly compared among each other on a magnitude scale. For [[Solar System]] bodies that shine in reflected light, a different definition of [[Absolute magnitude#Solar System bodies (H)|absolute magnitude (H)]] is used, based on a standard reference distance of one [[astronomical unit]].

Absolute magnitudes of stars generally range from approximately −10 to +20. The absolute magnitudes of galaxies can be much lower (brighter).

The more luminous an object, the smaller the numerical value of its absolute magnitude. A difference of 5 magnitudes between the absolute magnitudes of two objects corresponds to a ratio of 100 in their luminosities, and a difference of n magnitudes in absolute magnitude corresponds to a luminosity ratio of 100<sup>n/5</sup>. For example, a star of absolute magnitude M<sub>V</sub> = 3.0 would be 100 times as luminous as a star of absolute magnitude M<sub>V</sub> = 8.0 as measured in the V filter band. The [[Sun]] has absolute magnitude M<sub>V</sub> = +4.83.<ref name="SunAbs"/> Highly luminous objects can have negative absolute magnitudes: for example, the [[Milky Way]] galaxy has an absolute [[UBV photometric system|B magnitude]] of about −20.8.<ref name="Karachentsev"/>

As with all astronomical [[magnitude (astronomy)|magnitudes]], the absolute magnitude can be specified for different [[wavelength]] ranges corresponding to specified [[Filter (optics)|filter]] bands or [[passband]]s; for stars a commonly quoted absolute magnitude is the '''absolute visual magnitude''', which uses the visual (V) band of the spectrum (in the [[UBV photometric system]]). Absolute magnitudes are denoted by a capital M, with a subscript representing the filter band used for measurement, such as M<sub>V</sub> for absolute magnitude in the V band.

An object's absolute ''bolometric'' magnitude (M<sub>bol</sub>) represents its total [[luminosity]] over all [[wavelengths]], rather than in a single filter band, as expressed on a logarithmic magnitude scale. To convert from an absolute magnitude in a specific filter band to absolute bolometric magnitude, a [[bolometric correction]] (BC) is applied.<ref name="Flower1996"/>