The phenomenon was observed between 12.10pm and 12.40pm when the fifth and penultimate phase of assembly elections was underway in parts of Kolkata. (File photo)

KOLKATA: A red and blue ring around the sun, popularly known as '22 degree circular halo' was sighted on Saturday afternoon in the city.

The phenomenon was observed between 12.10pm and 12.40pm when the fifth and penultimate phase of assembly elections was underway in parts of the city.

The phenomenon popularly known as the 22 degree circular halo of the sun or occasionally the Moon (also called a moon ring or winter halo), occurs when the sun's or moon's rays get deflected/ refracted through the hexagonal ice crystals present in cirrus clouds, a senior researcher with the MP Birla Planetarium told PTI today.

"These kind of cirrus clouds are generally formed when water vapour freezes into ice crystals at altitudes five to ten kilometres above the earth's surface," the researcher said.

"It's a very common phenomenon in the cold countries. But in our countries it's occurrence is rare and cannot be predicted ... The red and blue ring around the sun was seen for around 30 minutes," he added.

The 22 degree halo was last observed in April 2013 in the suburbs of the city, the meteorologist said, adding, the phenomenon takes place before an impending storm.

