Spectral Classification Characteristics

Spectral Class Color Surface Temperature (K) Principal Features Examples
O Bluish-white 30,000-50,000+ Relatively few absorption lines. Lines of ionized helium and other lines of highly ionized atoms. Hydrogen lines appear only weakly. Peak of light in UV part of spectrum. Naos
B Bluish-white 10,000-30,000 Lines of neutral helium. Hydrogen lines more pronounced than in O-type stars. He I lines strong, as well as C II, O II, Si III. Rigel, Spica
A Bluish-white to white 7,500-10,000 Strong lines of hydrogen. Also lines of singly ionized magnesium, silicon, iron, titanium, calcium, and others. Lines of some neutral metals show weakly. Sirius, Vega
F white to yellowish-white 6,000-7,500 Hydrogen lines are weaker than in A-type star but still conspicuous. Lines of singly ionized metals are present (Ca II), as are lines of other neutral metals. Canopus, Procyon
G yellow to yellowish-white 5,000-6,000 Lines of ionized calcium (Ca II) are the most conspicuous. Many lines of ionized and neutral metals are present. Hydrogen lines are weaker even than in F-type stars. Sun, Capella
K yellowish-orange 3,500-5,000 Lines of neutral metals predominate. Hydrogen very weak, molecular bands start to appear. Arcturus, Aldebaran
M reddish 2,200-3,500 Strong lines of neutral metals and molecules. Betelgeuse, Antares
L red 1,400-2,200 Visible mainly in the infrared part of the spectrum. Strong lines of neutral metals and molecules, including water, CO, TiO, FeH, O2. *
T red Less than 1,400 Visible almost entirely at Infrared wavelengths, shows strong methane features. *
* Stars of L and T types are so cool and faint that there are no well known examples of them visible to the unaided eye.

Obsolete Spectral Classifications

Spectral Class Color Surface Temperature (K) Principal Features
R orange to red 4000 Strong CN features, and C2 features increasing in strength. Often catagorized as a C (Carbon) star.
N red 3000 C2 present, with CN decreasing in strength. Often catagorized as a C (Carbon) star.
S red 3000 Excess of heavy elements, molecules of ZrO, YO, KaO