A chance gaze to the skies in Kolkata on Friday morning would have revealed a bright ring around the sun, an atmospheric phenomenon called a 22 degree halo of the sun, which lasted nearly an hour.
“There is no way that the phenomenon can be predicted as it entirely depends on atmospheric conditions. So anyone who looked up at the sky when the ring was formed and saw it, was just lucky to have done so,” said Dr. D.P. Duari, Director (Academic and Research) of the Birla Planetarium.
Caused by the presence of a particular kind of clouds in the atmosphere, the phenomenon is spectacular, but not particularly rare.
“The phenomenon occurs whenever a particular kind of cloud is present in the atmosphere. These clouds — characterised by thin strands — are called cirrus clouds,” Dr. Duari said.
The cirrus clouds are formed at a height of between five and 10 km above the earth's surface.
At that height, water vapour freezes into ice crystals within these clouds. These ice crystals, usually hexagonal in shape, refract sunlight at an angle of 22 degrees, causing a ring-like shape, he added.
