Astrophysics (index)about

Spectral Class

(Spectral Type, Stellar Class, Stellar Type, Star Class, Star Type)
(classification of spectrums of stars (O, B, A, etc.))

A star's Spectral Class (or Spectral Type), a categorization based on features of its spectrum, primarily depends upon its Surface Temperature. The terms Early and Late are used to mean hotter and colder, e.g., "O", "B", and "A" are considered to be "early" classifications, and a star with an Effective Temperature of 3600K would be considered an "early" M-class star. The terminology arose at a time when it was imagined that stars cool as they age.

The classes are useful for relating the spectrum of Main Sequence Stars with their Mass, Radius, and Luminosity


Classconventional colorSurface tempMassRadiusLuminosityHydrogen Spectral LinesAbundance
O-Type Starhottest"blue">33000K>16 Msun>6.6Rsun>30000Lsunweak.00003%
B-type Star"blue-white"10000-33000K2.1-16Msun1.8-6.6Rsun25-30000Lsunmedium.13%
A-type Star"white"7500-10000K1.4-2.1Msun1.4-1.8Rsun5-25Lsunstrong.6%
F-type Star"yellow-white"6000-7500K1.04-1.4Msun1.15-1.4Rsun1.5-5Lsunmedium3%
G-Type Star"yellow"5200-6000K.8-1.04Msun.96-1.15Rsun.6-1.5Lsunweak7.6%
K-Type Star"orange"3700-5200K.45-.8Msun.7-9.6Rsun.08-.6Lsunvery weak12.1%
M-Type Star"red"2000-3700K<.45Msun<.7Rsun<.08Lsunvery weak76.56%
L-Type Star"purple-red"1300-2000K???extremely weakn/a
T-Type Star"brown"700-1300K???extremely weakn/a
Y-Type Starcoolest"dark brown"<700K???extremely weakn/a

Numbers 0-9 are appended to break down classes further.

The mnemonic for the sequence OBAFGKM is "Oh Be A Fine Girl Kiss Me".


Referenced by:
Absorption Line
A-type Star (A)
AD Leonis (AD Leo)
Algol (Beta Per)
Alpha Centauri
Astronomical Quantities
Barnard's Star
B-type Star (B)
Beta Centauri
Binary Star
Brown Dwarf (BD)
Epsilon Eridani
Epsilon Indi (ε Indi)
F-type Star (F)
FGK Star
51 Pegasi b (51 Peg b)
G-Type Star (G)
HR 8799
Kapteyn's Star
K-Type Star (K)
Lacaille 9352
Lalande 21185
L-Type Star (L)
LHS 1140
Luhman 16
Luminosity Class
Luyten 726-8
M-Type Star (M)
Morgan Classification
O5 Spectral Class (O5)
OB Association
O-Type Star (O)
Red Giant
Ross 154
Ross 248
Scholz's Star
Spectroscopic Parallax
Standard Candle
Star Count
Stellar Association
Stellar Distance Determination
Stellar Luminosity Determination
Stellar Mass Determination
Stellar Temperature Determination
T-Type Star (T)
T Tauri
Variable Star
WISE 0855-0714
WISE 1506+7027
Wolf 359
Y-Type Star (Y)