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In astronomy, absolute magnitude (M) is a measure of the luminosity of a celestial object on an inverse logarithmic 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 ...
For example, 3C 273 has an average apparent magnitude of 12.8 (when observing with a telescope), but an absolute magnitude of −26.7. If this object were 10 parsecs away from Earth it would appear nearly as bright in the sky as the Sun (apparent magnitude −26.744).
In astronomy, the apparent brightness of a star, or any other luminous object, is called the apparent magnitude. The apparent magnitude depends on the intrinsic brightness (also called absolute magnitude) of the object and its distance. If all stars had the same luminosity, the distance from Earth to a particular star could be easily determined.
An illustration of light sources from magnitude 1 to 3.5, in 0.5 increments. In astronomy, magnitude is a measure of the brightness of an object, usually in a defined passband. An imprecise but systematic determination of the magnitude of objects was introduced in ancient times by Hipparchus. Magnitude values do not have a unit.
The main sequence is sometimes divided into upper and lower parts, based on the dominant process that a star uses to generate energy. The Sun, along with main sequence stars below about 1.5 times the mass of the Sun (1.5 M ☉), primarily fuse hydrogen atoms together in a series of stages to form helium, a sequence called the proton–proton chain.
For nearby objects (say, in the Milky Way) the luminosity distance gives a good approximation to the natural notion of distance in Euclidean space. The relation is less clear for distant objects like quasars far beyond the Milky Way since the apparent magnitude is affected by spacetime curvature , redshift , and time dilation .
There is also a significant increase in luminosity, reaching an absolute magnitude of −19.3 (or 5 billion times brighter than the Sun), with little variation. [87] The model for the formation of this category of supernova is a close binary star system.
The brightness usually refers the object's absolute magnitude, which, in turn, is its apparent magnitude at a distance of one astronomical unit from the Earth and Sun. The phase curve is useful for characterizing an object's regolith (soil) and atmosphere. It is also the basis for computing the geometrical albedo and the Bond albedo of the body.