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B Question about Hertzsprung-Russell-diagram

  1. Mar 27, 2017 #1
    Why can you read out the radii of the stars by knowing their temperature and luminosity?
    Can't make sense out of it.

    Attached Files:

  2. jcsd
  3. Mar 27, 2017 #2


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    The Stefan-Boltzmann equation tells you the amount of radiation emitted from a unit area of the star as a function of temperature. The total luminosity is then given by just summing this over the surface area of the star, so:

    [tex] L = \sigma T^4 * 4 \pi R^2[/tex]

    So if you know L and T, you can calculate R.
  4. Mar 27, 2017 #3
    wow that was easy thanks!
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