Kolkata: People in Kolkata and its surroundings got a celestial treat on Wednesday morning at around 10:45 am, as they looked up in the sky towards the sun.
A spectacular ring of light was seen surrounding the sun. The ring was a perfect circle with the sun at the centre. This absolutely dazzling 'halo' of the sun was observed till noon.
People were enthralled and excited by this celestial sight, which was evident as photographs of the phenomenon went viral on social networking sites.
"The 22 degree halo of the sun" as it is called, because the angular distance of the light ring is exactly 22 degrees from the sun at the centre, occurs because of the interaction of sunlight with ice crystals suspended in the air in a particular type of cloud.
"The ice crystals responsible for the halos are typically suspended in cirrus or cirrostratus clouds in the upper troposphere, which are typically present at a height of 5-8 km from the earth's surface," said Debiprosad Duari, director, research & academic, MP Birla Planetarium.
According to Duari, the particular shape and orientation of the crystals are responsible for the type of halo observed. It is hypothesised that the ice crystals present in the cirrus clouds are typically hexagonal in shape. When the sunlight falls on these crystals, it gets refracted while passing through hexagonal crystals and gets bent by 22 degrees or more. As a result, a bright ring of light forms around the sun at an angle of 22 degrees.
The 22 degree halo of the sun can occur whenever there are moisture-laden cirrus clouds in the sky near the sun and it is a local phenomenon.
This is not a very rare phenomenon and happens quite regularly at different places, depending upon favourable atmospheric conditions. The duration of the 22 degree halo of the sun depends on the cloud formations and the air currents in the atmosphere.