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Diffraction - central spot covers moon

  1. Nov 1, 2012 #1
    1. The problem statement, all variables and given/known data
    The Moon is about 4x10^8 m from the Earth and has a diameter of about 3.2x10^6 m. You want a radar which just covers the Moon with the central spot of its diffraction pattern. If the radar has a wavelength of 16.5cm , what is the diameter of the radar antenna?



    2. Relevant equations
    Circular Aperture D=(2.44*λ*L)/(diameter of the moon)
    D=diameter of the radar



    3. The attempt at a solution
    plugging in the values I found D=(2.44*(16.5*10^-2)*(4x10^8))/(3.2x10^6) and D=50.325m, which is incorrect.


    Am I making any incorrect assumptions, or is it the incorrect formula to be using for this type of problem.

    Thanks
     
  2. jcsd
  3. Nov 1, 2012 #2

    haruspex

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    Can you tell me where the 2.44 comes from? Maybe a URL?
     
  4. Nov 8, 2012 #3
    no worries figured it out
     
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