Angular Resolution of a Telescope

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    Michael E. Marotta

    Angular resolution in radians = 1.22 times the quotient (wavelength / aperture) 

    Make sure to keep the units the same, wavelength may be in angstroms; aperture may in inches. So, do the conversions first.

    For example, a telescope with a 10-inch lens is assumed to be observing in the visible spectrum. Assume the middle range. The last step is to convert radians to arc seconds.

    Answer: 0.54 arc seconds.

    My telescope has an aperture of 102 mm.

    Answer ranges 0.98″ (violet) to 1.72″ (red)

    Michael E. Marotta

    The example comes from  A Student’s Guide to the Mathematics of Astronomy by Fleisch & Kregenow, Cambridge University Press, 2013.

    Paul Leyland

    You give the accurate (and correct) procedure.  For a decent approximation I just divide 140 by the aperture in mm, which gives an answer which is “good enough”.  In your case 140/102 = 1.37.

    Easy to remember.

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