Hertzsprung- Russell diagram13.7 - Be able to sketch a simple Hertzsprung-Russell diagram, including labelled axes and indicate the positions of the following:
a) main sequence stars
b) the Sun
c) red and blue giant stars
d) white dwarf stars
e) supergiant stars
13.8 - Understand how a star’s life cycle relates to its position on the Hertzsprung-Russell diagram, for stars similar in mass to the Sun and those with masses that are much greater
13.13 - Understand how to use a Hertzsprung-Russell diagram to determine distances to stars
Hertzsprung and Russell were two astronomers who, independently of each other, produced a diagram that shows the relationship between a star's temperature and luminosity.
The diagram has a prominent diagonal band called the 'main sequence' Here there are stars such as our own with a range of temperatures and luminosity.
Cooler but brighter stars appear as giants toward the top right, while hotter but dimmer stars appear as dwarfs in the bottom left.
We can plot the pattern of a star's evolution on this diagram.
A star like our own will swell to become a giant and then dim to become a white dwarf.
Astronomers use spectroscopic parallax to estimate the spectral type of a star. They calculate the luminosity of the star and can work out its distance using its apparent brightness. They can then place it on the H-R diagram and find it's absolute magnitude.
We calculate the size of a star using Stefan's Law which relates luminosity and temperature to its radius.
Try to remember these main components of the diagram:
- Spectral Class (OBAFGME)
- Position of Sun (G - Main sequence)
- Shape of main sequence
- Position of giants & super giants
- Position of white dwarfs
|Star||Stellar class||Apparent magnitude||Absolute magnitude||Distance (ly)|
|α Centauri A (HD 128620)||G2V||0.01||4.38||4.36|
|α Centauri B (HD 128621)||K1V||1.34||5.71||4.36|
|Wolf 359 (CN Leonis)||M6.0V||13.44||16.55||7.85|
|Luyten 726-8 A||M5.5Ve||12.54||15.4||8.79|
|Luyten 726-8 B||M6.0Ve||12.99||15.85||8.79|