Halo

Halo usually appears around the Sun or moon, sometimes around other powerful light sources such as street lights. There are many types of halos, but they are mostly caused by ice crystals in Cirrus clouds at a height of 5-10 km in the upper troposphere. The form of the observed halo depends on the shape and arrangement of crystals. Reflected and refracted by the ice crystals, the light often turns into a spectrum, which makes halo look like a rainbow, but a halo in low light has a low chroma, which is associated with the peculiarities of twilight vision.
Sometimes in frosty weather, the halo is formed by the crystals is very close to the earth's surface. In this case, the crystals resemble sparkling gemstones.
It is necessary to distinguish halo from crowns. The latter have a smaller angular size (up to 5°), and due to diffractive scattering rays of light in water droplets forming a cloud or fog.
Halo has a diverse number of forms, so it is mistaken for many different phenomena: UFOs, ghosts, new heavenly bodies, living organisms, plasma, etc.

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