Although our limited eyes cannot detect purple stars, the color purple is nevertheless part of a skywatcher’s vocabulary. It becomes especially noticeable when we deal with atmospheric aberrations, lensing effects, and the scattering of light.

Purple halos around stars can be a problem when shooting with inexpensive camera lenses and telescopes. They come about when refractive optics — optics that contain lenses — don’t focus blue and red wavelengths of light at the same place as the rest of the visual spectrum.