Download Hertzsprung Russell diagram

The Hertzsprung-Russell diagram
Spectral type: O
B
A
F
Absolute magnitude
G
K
M
Luminosity
(Sun = 1)
Red supergiants
10000
Rigel
Betelgeuse
-5
Spica
1000
Antares
Red giants
0
100
Aldebaran
Arcturus
Vega
10
Sirius A
Sun
1
+5
Main sequence
10-1
10-2
+10
10-3
Kapteyn’s star
White dwarfs
10-4
Sirius B
+15
Surface temperature (K):
Procyon B
40000
20000
10000
6000
4000
3000
2000
Early in the twentieth century (around 1910) two astronomers, Ejnar Hertzsprung and Henry
Russell first had the idea of plotting the absolute magnitude of a star against its spectral type.
This type of diagram is known as a Hertzsprung-Russell diagram. Since the original diagram
was produced other quantities, the surface temperature and the luminosity compared with
the Sun, have been added to give a version like that shown here. It is a very useful way to
display the properties of a star.
Hot bright stars are towards the top left of the diagram while cool and dim stars are towards
the bottom right. Some stars, like the supergiants are quite cool but because of their
enormous size they are in the top right of the diagram. On the other hand white dwarfs are
hot small stars and so appear to the bottom left.
There is a band of stars that runs from the top left to the bottom right (shown by the dotted
line in the diagram) and this is called the Main Sequence. Stars that lie in this area are called
main sequence stars – the Sun is a main sequence star. In a way stars that lie on the main
sequence are ‘normal’ stars while those that lie to one side or other of this area are ‘unusual’
stars – these stars such as white dwarfs, red giants and supergiants. Notice that supergiant
stars can be either hot like Spica or cool like Betelgeuse. About 90% of the stars in our
region of the galaxy are main sequence stars, 10% are white dwarfs and 1% are red giants
or supergiants.