Suppose two distant sources of light are separated by angle $$ when viewed from the center of a circular aperture. Each source creates a diffraction pattern, and the two central maxima are separated by the same angle $.$ If $$ is large, there will be two distinct bull's$-$eye patterns and you can tell, just by looking at the screen, that there are two sources. If $$ is very small, the diffraction patterns will overlap so much that you cannot observe two distinct sources. The two sources will be marginally resolved, which means that you can just barely detect two sources, if the central maximum of one diffraction pattern falls on the first minimum of the other diffraction pattern$--$that is$,$ if $=$$1=1\mathrm{.}22$$/$D$=$$1=1\mathrm{.}22$$/$D$.$ The Arecibo Observatory in Puerto Rico was a $310-$mm$-$diameter radio telescope that collapsed in $2020.$ Incoming radio waves reflected from the receiving dish rather than passing through it$,$ but the laws of diffraction work the same in both cases.