Quick Reference
ASTRONOMY - SPECTRAL CLASSES
The Solar System | Star Formation | Celestial Bodies | Spectral Classes
Spectral Class |
Tempterature - Colour |
Principal Characteristics |
| O | 25,000 K - Blue | This stage is characterized by lines of helium, oxygen, and nitrogen in the spectrum of the photosphere. O stars are extremely hot, very bright stars that emit large amounts of ultraviolet radiation. |
| B | 11,000 K - 25,000 K - White-blue | In this group the lines of helium in the spectrum reach a maximum intensity and then fade. The intensity of the hydrogen lines regularly increases in all the subdivisions of stage B. Type B stars are typically represented by the star Epsilon Orionis. |
| A | 7500 K - 11,000 K - White | This group comprises the so-called hydrogen stars. The spectra of these stars is dominated by absorption lines of hydrogen. Sirius, the Dog star, is a typical type A star. |
| F | 6000 K - 7500 K - Yellow-white | This group is composed of stars characterized by an elevated intensity of the H and K lines of calcium and of lines characteristic of hydrogen. A notable star in this category is Delta Aquilae. |
| G | 5000 K - 6000 K - Yellow | This group is composed of stars with prominent H and K calcium lines and less prominent hydrogen lines. The spectra of numerous metals, in particular iron, are also present. The Sun belongs to this group, and therefore G stars are frequently called solar stars. |
| K | K 3500 K - 5000 K - Orange-yellow | This group comprises stars having strong calcium lines and lines indicating the presence of other metals in their spectra.The violet light of class K stars is less intense than the stars' red light. This group is typically represented by Arcturus. |
| M | 3500 K - Red | This group is composed of stars whose spectra are dominated by bands resulting from the presence of metallic-oxide molecules, notably those of titanium oxide. The violet end of the spectra is less intense than that of K stars. The star Orionis is typical of this group. |
