Stellar classification

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In astronomy, stars are classified into different types depending on their spectra; this is connected to other properties of the star such as temperature and apparent color. Currently, there are seven main types, which are in order of decreasing temperature: O, B, A, F, G, K, and M.

The classes

Class	Characteristics	Color	Temperature in K	Typical mass for main sequence (M☉)	Star samples
O	ionized Helium (He II)	blue	30000–50000	>18	Mintaka, Naos
B	neutral Helium (He I), Balmer-Series hydrogen	blue-white	10000–30000	5	Rigel, Spica, Achernar
A	Hydrogen, Calcium (Ca II)	white	7500–10000	1,9	Vega, Sirius, Altair
F	Calcium (Ca II), occurrence of metals	white-yellow	6000–7500	1,4	Prokyon, Canopus, Polaris
G	Calcium (Ca II), iron and other metals	yellow	5300–6000	1,0	Tau Ceti, Sun, Alpha Centauri A
K	strong metal lines, later Titanium dioxide	orange	3900–5300	0,7	Arcturus, Aldebaran, Epsilon Eridani, Albireo A
M	Titanium(II)-oxide	red-orange	2300–3900	0,3	Betelgeuse, Antares, Kapteyn's Star, Proxima Centauri