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Physics - Formulas - Magnitudes

A Magnitude is the measure of brightness of a celestial object. It is a logarithm scale that is used to determine levels of brightness between other stars. The ratio of apparent brightness between two stars is:

There are actually two types of Magnitude: apparent and absolute. Apparent magnitude is the how bright a star looks from Earth. Absolute magnitude is the true brightness of a star.

When comparing the apparent and absolute magnitude of a star, we get what is called the Distance Modulus:

This is actually a very powerful equation in that if we know the absolute and apparent magnitude of a star, we can determine its distance - and its pretty accurate too.

In addition to comparing stars, we can also compare color ratios between stars to learn surface temperature. This color ratio is also called a B-V ratio (B=blue, V=visual or green) that is determined by using filters (Blue and Green in this case):

For example, a star with a V < B ratio, the surface temperature is higher than a star with a V > B ratio. As a note, other filters can be (and often are) used.

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