Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Spectrum of the Sun vs black body

  1. Sep 1, 2011 #1

    fluidistic

    User Avatar
    Gold Member

    In wikipedia I've read that the Sun's surface temperature is about 5700K.
    The emission spectrum graph can be seen there: http://en.wikipedia.org/wiki/File:EffectiveTemperature_300dpi_e.png.
    I don't understand why the irradiance (or intensity I guess) of the Sun is greater than the one of a black body at 5700K. This would imply that the emissivity of the Sun is greater than 1, which is impossible. What am I missing?
     
  2. jcsd
  3. Sep 3, 2011 #2

    chemisttree

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Must be that the Sun's emission spectrum has more going on than just blackbody radiation.
     
  4. Sep 4, 2011 #3
    It's just that the sun is not a blackbody. In other portions of the same curve, the ratio is less than 1. The 5700 number comes from a single-parameter fit to the actual spectrum, and does not mean that the sun really is a blackbody with a temperature of 5700K. At short wavelengths especially, it looks nothing like a blackbody.
     
  5. Sep 4, 2011 #4

    fluidistic

    User Avatar
    Gold Member

    I understand. But the Sun's surface is at 5700K, right? If I consider the Sun as a gray body then I should expect its irradiance to be lesser than the one of a blackbody at the same temperature, for all wavelengths. Am I right on this? If so, I still have trouble understanding the graph.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Spectrum of the Sun vs black body
  1. Black hole black body (Replies: 2)

  2. Black dwarf sun (Replies: 3)

Loading...