Different stars have different spectra or light curves. This means we can classify stars by their spectral class, with stars emitting the same type of spectrum belonging to the same spectral class – roughly speaking, every spectral class corresponds to a different surface temperature.
Every spectral class is given a different letter. These are, in order of decreasing surface temperatures O,B,A,F,G,K and M.
|
Class |
Effective Surface Temperature (K) |
Colour |
|
O |
28,000 – 50,000 |
Blue |
|
B |
9,900 – 28000 |
Blue – white |
|
A |
7,400 – 9,900 |
White |
|
F |
6,000 – 7,400 |
Yellow – white |
|
G |
4,900 – 6,000 |
Yellow |
|
K |
3,500 – 4,900 |
Orange |
|
M |
2,000 – 3,500 |
Orange - red |
The main spectral classes can be subdivided.
One way of determining the spectral class of a star is to look at the relative intensity of different lines in the spectrum of the star. Different relative intensities correspond to different spectral types.
