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Spectral Classifications
Type Color Major Spectral Features Temp [K] Examples
O5-O9 Blue-Violet  Few lines.  He II present.  OII, OIII, NII, NIII, CII and CIII sometimes present. H 
    Balmer lines and HeI lines weak but present.		 30000-50000 δ Orionis
B0-5 Blue-White  H Balmer lines stronger than in O types.  HeII, OIII, NIII and CIII absent.  HeI
    relatively strong, reaching maximum strength in type B2.  OII and NII usually
    present.  HeI λ4026Å and λ4471Å are nearly as strong as H Balmer lines in type
    B0 but are barely visible in B5. 		28000-15000 Spica (B1)
B8 Blue-White  HeI lines weaker than in B0-5.  Ionized Ca, Mg, Fe appear.  H Balmer lines
    stronger than in B0-5.		 12000 Regulus (B7) Rigel
A0-A9 White  H Balmer lines at maximum strength.  He absent.   Ca II K + Hδ (blended) is barely
    detectable in A0 but increases rapidly as type gets later.  By A5 CaII K is about
    : the strength of CaII H + Hε (also blended).		 9900-7500 Vega (A0) Sirius (A1) Denebola (A3) Altair (A7)
F0 Yellow-White  H Balmer lines are weaker than in type A, but still very strong.  G-band (λ4305Å) is
    yet invisible.  Ionized metal lines are increasing in strength.  CaII K is slightly
    weaker than CaII H + Hε.		 7400 Canopus
F5 Yellow-White  H Balmer lines are weaker than in F0, but still strong.  Ionized metal lines stronger than in type F0.  CaII K is about equal in strength to CaII H +  Hε.  The G-band is about ½ the strength of Hγ . 6600 Procyon
G0 Yellow  G-band is stronger than Hγ .  H lines weakening but easily visible.  Ionized metallic lines stronger. 6000  
G2 Yellow  Type of sun.  CaII H and K are strongest lines present. 5800 Sun
G5 Yellow  G-band very strong.  It produces a perceptible break in the continuum.  Hδ weak or even absent.  CaI λ4226Å not yet detectable. 5500  
G8 Yellow-Orange   5200 Capella
K0 Orange  Well developed break in the continuum at the G-band.  G-band much stronger than CaI λ4226Å.  CaII H and K lines are near their maximum strength. 4900 Arcturus
K5 Orange  CaI λ4226Å stronger than G-band.   No TiO bands yet visible.  Metals very strong. 4100 Aldebaran
M0 Red-Orange  TiO bands present.  Band head degraded to red visible at λ4950Å. 3500  
M5 Red  TiO completely dominant.  TiO band heads degraded to red present at λ4950Å, λ4760Å and λ4585Å. 2800 Betelguese (M2)
M8 Red   2500  
L Red   1300-2500 (Brown dwarfs)
T Red   <1300