Physlet Illustration: Blackbody Radiation

 

 
Temperature = K                   
This simulation illustrates the fact that the distribution of energy from a blackbody radiator depends only upon its temperature.  Consider the circle of light shown above the word "appearance" to be a star seen through a telescope.  The three circles above the "star" show the relative energy density observed through red, green, and blue filters.  The user may specify the maximum wavelength by clicking on the graph or the temperature by entering in the box above.  How can astronomers determine the temperature of stars?  

Hints:

  1. Qualitatively, how does wavelength of maximum emission depend upon temperature?
  2.  How does this compare to Wien's Law?
  3. Typically one cannot measure the entire spectrum of a star.  Can one learn anything from the color of stars?
  4. Compare the color of a hot (50,000 K) "star" and a cool (2000 K) "star".  
  5. Compare the energy density through the three filters for hot and cool stars.  Do hot stars look bright through a particular filter?  Cool stars?  

Reference

See Walker, Sections 30-1

Illustration written by Chuck Niederriter