Convert apparent and absolute magnitude

Calculator for the apparent and absolute brightness of stars and other bright celestial bodies in magnitudes (mag). Apparent magnitude is what we see or perceive with measurements. The absolute magnitude would be that which the celestial body would have at a distance of 10 parallax seconds or parsecs (about 32.6 light years). So the absolute brightness says something about the real dimension. The apparent brightness, on the other hand, results from the absolute brightness and the distance from us.
Brightness is given in magnitudes (mag), the lower the value, the brighter. The scale is logarithmic, the Sun as the brightest object in the sky has an apparent magnitude of −26.74 mag, the planet Neptune is at +7.67 mag already below the perception threshold of the naked eye.
The absolute brightness can be calculated from the apparent brightness and distance. The formula is M = -5 * lg( r / 10pc ) + m with apparent magnitude m, absolute magnitude M, distance r and the common logarithm lg. Please enter the distance and one of the two brightnesses to calculate the other brightness.

Apparent brightness:		mag
Distance r:		mkmAUlypc
Absolute brightness:		mag

The units of distance are: m = meters, km = kilometers, mi = miles, AU = astronomical units, ly = light-years, pc = parsec

Examples: the Sun at a distance of 1 AU has an absolute magnitude of 4.82 mag. The star Deneb has an apparent magnitude of 1.25 and at a distance of 1550 light years an absolute magnitude of -7.13.

The apparent brightness is used more often because it tells us what we can see from Earth. The absolute brightness, i.e. the physical luminosity, can be expressed in mag as well as in multiples or fractions of the sun's luminosity. For example, the brightest star in the sky after the sun, Sirius, with an apparent magnitude of −1.46 mag and a distance of 8.7 light years, has an absolute magnitude of 1.41 mag and 25 times the luminosity of the sun.

Last updated on 06/30/2025. Author: Jürgen Kummer

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