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Stellarmagnitudes.ppt
Stellar classifications
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)
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.
Stellar Magnitude (brightness)
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!
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