Photometeors
(Section 3.2.3)Halo Phenomena
(Section 3.2.3.1)Definition: Halo phenomena: A group of optical phenomena in the form of rings, arcs, pillars or bright spots, produced by the refraction or reflection of light by ice crystals suspended in the atmosphere (cirriform clouds, diamond dust, etc.).
Halo types formed by refraction of sunlight may show colours, whereas reflection haloes are white. At night, it is difficult for the human eye to perceive colour; therefore, lunar haloes mostly appear white.