Absolute Magnitude

Absolute magnitude, as used in astronomy, is a measure of an object’s brightness at a distance of 10 parsec or 3.26 light years. This measure is used to easily characterize objects without giving too much information. For instance, apparent magnitude is also a measure of brightness but is dependent on the distance between the object and the observer.

If an object is nearer, it would be brighter and vice-versa. Thus, when reporting the brightness of an asteroid in terms of apparent magnitude, the observing distance must still be specified, whereas if it is reported in absolute magnitude, it is quickly understood that the observing distance is 3.26 light years. The use of absolute magnitude allows astronomers to compare observed luminosity without regard to distance.

Absolute magnitude is in the logarithmic scale of 100.4 or roughly 2.512, which means that object A that has an absolute magnitude of -25.5 is 10 times brighter than object B at -20 and 100 times brighter than object C at -14.5. In other words, if it were possible that object A and object B be viewed from the same distance, object A will be 10 times brighter than object B. Absolute magnitude can also be related to the size of the observed object but requires another quantity, the bolometric magnitude.

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