Data < Stellar Spectral Classes

In order of decreasing temperature, the original letters now run O, B, A, F, G, K, M. These stellar designations are called spectral classes (or spectral types). Use the time-honored mnemonic "Oh, Be A Fine Guy, Kiss Me" to remember them in the correct order

SPECTRAL CLASS SURFACE TEMPERATURE (K) PROMINENT ABSORPTION LINES FAMILIAR EXAMPLES
O 30,000 Ionized helium strong; multiply ionized heavy elements; hydrogen faint  
B 20,000 Neutral helium moderate; singly ionized heavy elements; hydrogen moderate Rigel (B8)
A 10,000 Neutral helium very faint; singly ionized heavy elements; hydrogen strong Vega (A0), Sirius (A1)
F 7,000 Singly ionized heavy elements; neutral metals; hydrogen moderate Canopus (F0)
G 6,000 Singly ionized heavy elements; neutral metals; hydrogen relatively faint Sun (G2), Alpha Centauri (G2)
K 4,000 Singly ionized heavy elements; neutral metals strong; hydrogen faint Arcturus (K2), Aldebaran (K5)
M 3,000 Neutral atoms strong; molecules moderate; hydrogen very faint Betelgeuse (M2), Barnard's Star (M5)

 
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