How can you determine a star's temperature, color, and expected size by knowing its spectral class?

I'm really confused in my science class! so can you explain to me about the different star spectral classes (O B A F G K M) and also how you determine the characteristics of a star by using these. Thanks :) 10 points best answerHow can you determine a star's temperature, color, and expected size by knowing its spectral class?The spectral classes (O,B,A,F,G,K,M, etc.) are in descending order of temperature. Temperature is directly related to color, so you know automatically that all M stars are red, K are orange, etc. If you find a red star is very bright, it must be a giant, since it is putting out less light per square centimeter of surface than hotter stars. If you find an A star that is intrinsically very faint, you know you are dealing with a white dwarf, since each square centimeter of surface is putting out a lot more light than a cooleer star (such as the Sun, a G star). Examples: Proxima Centauri is a normal red dwarf, the closest star to the Sun, but only visible with a telescope. Betelgeuse is a red giant, around 80 light years away but very bright. Sirius B is only 8.8 light years away, and hotter than the Sun, but only visible in a telescope, therefore a white dwarf (in fact, the first one discovered).

Plotting stars this way is in fact how Ejnar Hertzsprung and Henry Norris Russell developed the HR diagram.How can you determine a star's temperature, color, and expected size by knowing its spectral class?You can get this information from the charts in Wikipedia - Stellar Classification at: http://en.wikipedia.org/wiki/Spectral_cl鈥?/a>

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