| 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 |
Spectral Classification of Stars
Main sequence stars Stars can be classified into spectral classes according to their colour, temperature, or prominent absorption lines.