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

Homework Help: Astrophysics - star color index

  1. Sep 27, 2010 #1
    1. The problem statement, all variables and given/known data

    If a star emits the same intensity of radiation at all visible wavelengths, what will be its
    apparent color at the Earth’s surface?

    2. Relevant equations

    No equations....

    3. The attempt at a solution

    I realize that a horizontal line would occur through the visible spectrum if a curve was plotted on an intensity/wavelength diagram, however, considering there is no true peak in the visible colors, I have no idea what color is likely to be seen. I have thought that it might be white or black, but am not really confident with those answers. any help would be appreciated.
  2. jcsd
  3. Sep 27, 2010 #2
    Because human eyes are sensitive only to the visible spectrum, so narrow it down :wink:
    As you deduce, there are only 2 possible cases: white or black. When is a thing black to our eyes?
  4. Sep 27, 2010 #3
    we see black when light is not present. therefore, would this star have to be pure white? Then, because I am seeing it from Earth's surface, should I take into account the effects our atmosphere has on light, such as scattering? I think I am making this problem more difficult than it is.
  5. Sep 27, 2010 #4
    I also think you're making it more complicated than expected, but making problems complicated is crucial for reasoning :biggrin: Fortunately you're right in this case I think.
    Have a look at this: http://en.wikipedia.org/wiki/Diffuse_sky_radiation. I suppose that we don't have to gaze at the Sun :biggrin: so the intensity of light from the star here is small (we know that stars except the Sun are not so bright when observing from the Earth), i.e. we have to look directly to it. Since the shorter wavelength radiation is easier to be scattered by the atmosphere, what we receive if looking directly to the star is more of longer wavelength radiation.
    Anyway I'm no expert, so don't rely on my thought :biggrin: Justify it yourself :wink:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook