Stellar classifications

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Stellarmagnitudes.ppt
Stellar classifications
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Stellar Magnitude (brightness) Hipparchus
Defined the magnitude scale of stars by ranking
stars on a scale of 1 through 6, with 1 being the
brightest and six the dimmest. Using modern
tools, it was determined that the range of
brightness spanned a range of 100, that is, the
magnitude 1 stars were 100 times brighter than
magnitude 6. Therefore, each change in magnitude
corresponds to a factor of 2.512 change in
brightness, since (2.512)5 100 (to within
roundoff)
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Stellar Magnitude (brightness) Magnitude is the
degree of brightness of a star. In 1856, British
astronomer Norman Pogson proposed a quantitative
scale of stellar magnitudes, which was adopted by
the astronomical community. Each increment in
magnitude corresponds to an increase in the
amount of energy by 2.512, approximately. A fifth
magnitude star is 2.512 times as bright as a
sixth, and a fourth magnitude star is 6.310 times
as bright as a sixth, and so on.
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Stellar Magnitude (brightness)
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Stellar Magnitude (brightness) The naked eye,
upon optimum conditions, can see down to around
the sixth magnitude, that is 6. Under Pogson's
system, a few of the brighter stars now have
negative magnitudes. For example, Sirius is 1.5.
The lower the magnitude number, the brighter the
object. The full moon has a magnitude of about
12.5, and the sun is a bright 26.51!
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Stellar classifications
Bayer Designation. The star's designation
according to Bayer's Uranometria (1603). The
brightest star in a constellation is usually
designated as alpha, the second brightest as
beta, and so on. The Greek letter is then
typically followed by the constellation name
Alpha Gemini
Beta Gemini