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Star Classification

Spectral Classification

  • Originally we used a system based on the strength of hydrogen absorption lines
  • A new system was introduced based on decreasing temperature
    • Introduced by Annie Jump Cannon
    • Each class is further subdivided into 10 subclasses
      • Using numbers 0 through 9
    • Mnemonic for remembering:
      • Oh Be A Fine Girl, Kiss Me

Spectral Classes

Spectral ClassColourApproximate TemperaturePrinciple Features
OBlue>30,000 KNeutral and ionized helium lines, weak hydrogen lines
BBlue-white10,0000-30,000 KNeutral helium lines, strong hydrogen lines
AWhite7500-10,000 KStrongest hydrogen lines, weak ionized calcium lines, weak ionized metal lines
FYellow-white6000-7500 KStrong hydrogen lines, strong ionized calcium lines, weak sodium lines, many ionized metal lines
GYellow5200-6000 KWeaker hydrogen lines, strong ionized calcium lines, strong sodium lines, many lines of ionized and neutral metals
KOrange3700-5200 KVery weak hydrogen lines, strong ionized calcium lines, strong sodium lines, many lines of neutral metals
MRed2400-3700 KStrong lines of neutral metals and molecular bands of titanium oxide dominate
LRed1300-2400 KMetal hydride lines, alkali metal lines
TMagenta700-1300 KMethane lines
YInfrared< 700 KAmmonia lines

Luminosity Classes

Astronomy Star