F T

Thus a difference of one magnitude represents a ratio of 2.51 in flux. The logarithmic scale of astronomical magnitudes is actually a base 2.51 system.

This magnitude system is somewhat annoying. Fainter stars have larger numbers, and the logarithmic interval for unit magnitude (a factor of 2.51) is hardly conventional. A factor of 10, or 2, or e = 2.718, would be more natural. But one of the beauties of astronomy is its roots in human history; the oldest written records include astronomical references. The magnitude system is a daily tangible reminder of the observations of Hipparchus and astronomical history. But we could likewise perpetuate furlongs, rods, and pecks, and this definitely would not be convenient.

Spectral color bands

The magnitude of a star can be measured in any of a number of wavelength bands. Thus when specifying a magnitude, the spectral band that was measured is usually specified. The "3-color" system mentioned above is the traditional system often used, namely the UBV system: ultraviolet, blue, visual (yellow). Each spectral

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