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Star Spectrum and type. stellar classification is a classification of stars based on their spectral characteristics, what color of light is given from their photosphere
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stellar classification is a classification of stars based on their spectral characteristics, what color of light is given from their photosphere • We determine this by seeing what atomic excitations are most prominent in the light, giving an objective measure of the photosphere's temperature.
In the current star classification system, the Morgan-Keenan system, the spectrum letter also has a number from 0 to 9 indicating tenths of the range between two star classes, so that A5 is five tenths between A0 and F0, and A2 is two tenths of the full range from A0 to F0. Lower numbered stars in the same class are hotter. • Another dimension that is included in the Morgan-Keenan system is the luminosity class expressed by the Roman Numbers I, II, III, IV and V, expressing the width of certain absorption lines in the star's spectrum
Letters used to represent star type • O, B, A, F, G, K, and M • where O stars are the hottest and the letter sequence indicates successively cooler stars up to the coolest M class. • O stars are called "blue", B "blue-white", A stars "white", F stars "yellow-white", G stars "yellow", K stars "orange", and M stars "red",