Perrin (Perrin’s fringe)

Perrin's fringe is a subtle optical phenomenon observed when viewing a bright light source against a dark background, resulting in faint, colored or luminous edges surrounding the light. It occurs due to diffraction and interference effects of light waves interacting with imperfections or the boundary of the observing instrument. These fringes are often seen in astronomical observations, such as around the Moon or planets, and can reveal details about the light source or the instrument’s protective filters. Essentially, Perrin’s fringe is a delicate, visually observable pattern caused by the wave nature of light interacting with small structures or limits in optical systems.