A Division by zero isn't an infinite but an undefined result.
It's because If the divisor approaches zero from the negative side, the result tends to minus infinity.
I didn't take diffraction as an explanation because
A) the effect seems stronger on metals,
B ) the bright glow seems to be too defined, no ripples in intensity are visible (as seen in the slot experiment) and
C) I'm not able to find a photograph of the effect by Googling "visible diffraction"...
Today I was watching the full moon while I had one eye closed. There was a vertical metal rod which, by moving my head a bit, covered the moon completely, so that no direct light could hit my eye. (Yeah... I do things like that...)
I saw a thin line of moonlight parallel to the rod right at the...