What is the basis for the system of classification of stars?
by 
wickedwillie
ANSWERS: 1
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Classification of stars is rather complicated... There is a spectral classification (so to say by the color of the star), that started with empirical main classes of O, B, A, F, G, K, and M, which covers about 99% of all stars. The O-stars are the hottest, the M-stars are the coldest, which spans the range from blue-white (Rigel in Orion is B) to red (Antares is M). Then for the odd 1% some additional classes S, R, and N were conceived. Each class has up to ten subclasses (e.g. A0 - A9, K0 - K9, etc.). Then there may be appended letters like n, s, p that denote special features: A6s would mean that the spectral lines are "sharp", B0p would mean "peculiar". And finally there are prefixed letters like d for dwarf, g for giant, or c for high brightness. So gK9p would be a giant K9 star (yellow/orange) with a"peculiar" spectrum. Nowadays stars are often classified by their position in the so-called Hertzsprung-Russell diagram, basically a combination of absolute brightness and spectral class/surface temperature.
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