Starlight

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.