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Homework Help: Total extinction of light.

  1. Mar 27, 2013 #1
    1. The problem statement, all variables and given/known data

    I am given a distance at which a particular object is just discernible and am asked to find the opacity of the air.

    2. Relevant equations

    3. The attempt at a solutionI know that:


    but I don't know at what point you have total extinction. Obviously you would only have zero intensity with the density, opacity, or distance at infinity.

    I'm using Foundations of Astrophysics by Ryden and I can't find a reference to what intensity of light is not visible.
    Last edited by a moderator: Mar 28, 2013
  2. jcsd
  3. Mar 28, 2013 #2


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    Staff: Mentor

    A rough approximation might be sufficient. In that case, you can consider something like I(x)=1/e I_0 or I(x)=1/e^2 I_0.
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