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Transcript
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
