Hertzsprung- Russell diagram

13.7 - 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.

Determining Distance

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.

 

Animation
Summary

Try to remember these main components of the diagram:

  • Magnitude
  • Spectral Class (OBAFGME)
  • Position of Sun (G - Main sequence)
  • Shape of main sequence
  • Position of giants & super giants
  • Position of white dwarfs
Nearest Stars
Star Stellar class Apparent magnitude Absolute magnitude Distance (ly)
Sun G2V −26.74 4.85 0
Proxima Centauri M5.5Ve 11.09 15.53 4.24
α Centauri A (HD 128620) G2V 0.01 4.38 4.36
α Centauri B (HD 128621) K1V 1.34 5.71 4.36
Barnard's Star  M4.0Ve 9.53 13.22 5.95
Luhman 16A/B L8 10.7 14.2 6.5
WISE 0855−0714 Y2 25   7.26
Wolf 359 (CN Leonis) M6.0V 13.44 16.55 7.85
Lalande 21185 M2.0V 7.47 10.44 8.3
Sirius A A1V −1.46 1.42 8.65
Sirius B DA2 8.44 11.34 8.65
Luyten 726-8 A M5.5Ve 12.54 15.4 8.79
Luyten 726-8 B M6.0Ve 12.99 15.85 8.79
Ross 154  M3.5Ve 10.43 13.07 9.7
Ross 248  M5.5Ve 12.29 14.79 10.29
Epsilon Eridani K2V 3.73 6.19 10.44
https://en.wikipedia.org/wiki/List_of_nearest_stars_and_brown_dwarfs