## Spectral Classification of Stars

Main sequence stars Stars can be classified into spectral classes according to their colour, temperature, or prominent absorption lines.
 Spectral Class Colour Temperature °K Prominent Absorption Lines O blue 25,000 - 50,000 $H, \: He, \: He^{{}+{}}$ B blue 11,000 - 25,000 $He, \: H$ A blue white 7,500 - 11,000 $H$, ionised metals F white 6,000 - 7,500 ionised metals G yellow white 5,000 - 6,000 ionised and neutral metals K orange 3,000 - 5,000 neutral metals M red < 3,000 neutral metals, titanium oxide