Physicists list three conditions for halo to appear

The phenomenon was observed in Tatarstan a few days ago.

“The halo which could be seen recently is not a rare phenomenon for temperate latitudes. It indicates a humid air mass against a background of low temperatures. This was facilitated by the fact that we received the Arctic air mass with northern streams, which was colder than normal by 9 degrees Celsius. That is, the average daily temperature of the first ten-day period of January amounted to -19 degrees. Now we are at the top of winter, when the lowest temperatures are observed. At the same time, this phenomenon may be repeated in the future. It became possible to see it due to high atmospheric pressure and anticyclonic character of the weather,” explains Associate Professor of the Department of Meteorology, Climatology and Atmosphere Ecology Timur Aukhadeev.

Associate Professor of the Department of General Physics Rustam Daminov listed the three key conditions for a halo, “They are low temperature, a cloudless day, and high humidity. When humidity is high, small ice crystals form in the shape of hexagonal prisms, needles and plates smaller than snowflakes flying randomly in a cloud of air. Sunlight, reflected in the mirrored faces of the crystals, enters the surrounding space. The crystals themselves are not visible, but the light reflected from them we can notice. They rotate all 360 degrees, forming an arc-shaped curve or circle around the Sun. All this is explained by the law of geometrical optics.”

Halos can be observed year-round but are more frequent in winter. There are many types of halo, but they are mostly caused by ice crystals in fleecy clouds in the upper layers of the troposphere at an altitude of 5-10 km.

Sometimes halos can also take the shape of columns seen atop street lights – something which has also been observed recently in many Russian cities in the northern latitudes.