#icecrystals

A 22° halo and a circumhorizontal arc are two types of halos that are caused by the refraction of light by ice crystals in the atmosphere. They are both circular or arc-shaped optical phenomena that appear around or below the Sun or Moon. However, they have different characteristics and formation conditions.

A 22° halo is a white or colored ring that forms around the Sun or Moon at a radius of about 22 degrees. It is caused by the refraction of light by randomly oriented, hexagonal ice crystals in cirrus or cirrostratus clouds. The colors of the 22° halo are usually faint and red on the inside and blue on the outside. A 22° halo can be seen at any time of the year and at any latitude, as long as the Sun or Moon is not too high in the sky.

A circumhorizontal arc is a bright and colorful band that forms parallel to the horizon, below the Sun or Moon. It is caused by the refraction of light by plate-shaped, hexagonal ice crystals that are horizontally aligned in cirrus clouds. The colors of the circumhorizontal arc are more vivid and reversed from those of a rainbow, with red on top and violet at the bottom. A circumhorizontal arc can only be seen when the Sun or Moon is very high in the sky, at an elevation of 58 degrees or greater. This means that it is more common in tropical and subtropical regions, and rare or impossible in higher latitudes.

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The best part of the coldest days of winter is definitely being able to make these frozen bubbles! This one, with its golden, feathery crystals, is truly unique.

Halo (optical phenomenon)

Halo is the name for a family of optical phenomena produced by light interacting with ice crystals suspended in the atmosphere. Halos can have many forms, ranging from colored or white rings to arcs and spots in the sky. Many of these are near the Sun or Moon, but others occur elsewhere or even in the opposite part of the sky. Among the best known halo types are the circular halo (properly called the 22° halo), light pillars and sun dogs, but there are many more; some of them fairly common, others (extremely) rare.

The ice crystals responsible for halos are typically suspended in cirrus or cirrostratus clouds high (5–10 km, or 3–6 miles) in the upper troposphere, but in cold weather they can also float near the ground, in which case they are referred to as diamond dust. The particular shape and orientation of the crystals are responsible for the type of halo observed. Light is reflected and refracted by the ice crystals and may split up into colors because of dispersion. The crystals behave like prisms and mirrors, refracting and reflecting light between their faces, sending shafts of light in particular directions.

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