Why Stars Look FuzzySend light from a pin-point source through a round opening — a telescope, a camera, your pupil — and it never comes back to a point. It spreads into a bright central blob wrapped in faint rings: the Airy pattern. Two stars closer than the first ring blur into one, which is the hard limit on how sharp any lens can ever be. The journey: the pattern is the squared strength of the opening's Fourier transform, which for a circle is the Bessel function [2J₁(x)/x]². Fifteen wavelengths are added up, and because each colour’s rings sit at a slightly different radius, white light frays into coloured haloes. Pure fragment shader.