Measuring Stellar Luminosity
How do astronomers measure stellar luminosity?
Astronomers measure a star' luminosity using a scale of magnitudes that
has existed for well over a century. Polaris, the north star, is defined
as being magnitude 2.0. A star of first magnitude is 2.5 times brighter,
and a star of zero magnitude, like VGega, is 2.5 times brighter in turn
than a first magnitude star. This way, a fifth magnitude star, faintly
visible to the naked eye, is 100 times fainter than a first magnitude star.
Good question! Hope this answer works for you.
David H. Levy
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Update: June 2012