Named after its independent discovery in 1911 by Ejnar Hertzsprung and in 1913 by Henry Norris Russell. Exteme stars such as Wolf-Rayets (ST ~100,000 K) and cool, dim dwarfs (ST~1000 K) have been omitted from this diagram.
The diagram gives a rough indication of SIZE. Stars in the top right of the diagram are giants, whereas those in the lower left are dwarfs. COLOUR is also indicated, blue being on the left and red on the right. The Main Sequence in the middle is the line where stars spend the majority of their life. The more massive the star, the shorter this life span is. The Sun can expect to spend around 9,000,000,000 years on the main sequence before evolving off it. This is the average for stars.
Type |
Line Appearances |
Temperature Range |
W |
Emission lines, WN(nitrogen),WC(carbon) | 60 - 100,000 K |
O |
Emission lines, He II | 30 - 50,000 K |
B |
No emission but H & He I absorption lines | 10 - 30,000 K |
A |
Hydrogen lines dominate | 7.3 - 10,000 K |
F |
H, neutral metals, especially Ca | 6.0 - 7,300 K |
G |
Weaker H, ionized Ca II & neutral metals | 5.0 - 6,000 K |
K |
Weak H, strong metallic, CaI, CaII, molecular | 3.5 - 5,000 K |
M |
Many molecular bands, Titanium oxide present | 2.5 - 3.500 K |
C |
Formally R, N. Carbon lines, variable spectra | ~2500 K |
S |
Zirconium & Titanium oxide bands | ~2500 K |
Q |
Reserved for Novae |
(NB: in table, metal = any element heavier than Helium)