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I have this question asking me to decided whether we can view a a crater on the moon given the turbulence in the atmosphere turns a point source into an extended source of diameter 1". We also found the diffraction limit of the telescope to be 0.57". Now I am confused about why we cant observe this crater on the moon - we know it subtends an angle of 0.93":

  1. this is greater than the minimum angular resolution of the telescope.

  2. the turbulence increases its diameter (due to its affect on the point source), so the angle subtended is still greater than minimum angular resolution implying it can be resolved?

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Here's a plot of 36 point sources spread out to gaussians of variance 0.1 spread out evenly on a ring of radius 0.93:

Mathematica graphics

Here's a plot of that same ring of point sources, but now with a variance of 0.57:

Mathematica graphics

Here's a plot of that same ring of point sources, but now with each point source broadened to a gaussian with variance 1:

Mathematica graphics

You tell me whether your telescope will be able to resolve that crater or not.

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  • $\begingroup$ so am I write in thinking that the maximum turbulence for us to be able to remove the crater is if it increase point sources to a diameter of 0.36" $\endgroup$ – DLB Apr 9 '18 at 10:41
  • $\begingroup$ @DLB I don't know how you got that number, but what matters isn't particularly the final number but rather the method that you're using. Without that, there's very little critique that anyone can offer about its correctness. $\endgroup$ – Emilio Pisanty Apr 9 '18 at 11:34

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