combined magnitude

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The total brightness of two (or more) celestial objects, such as a close pair of stars that appear as one to the naked eye. Since the magnitude scale is logarithmic, the combined magnitude m is not simply the sum of the individual magnitudes m1 and m2, but must be found from the formula

m = m1 −2.5 log {1 + antilog[ −0.4 (m2m1)]}

For example, the combined magnitude of two stars each of magnitude 1 is 0.25.

Subjects: Astronomy and Astrophysics.

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