Citizens in parts of Kolkata were enthralled to witness a spectacular phenomenon of a perfect rainbow ring or ‘halo’ this morning.
The phenomenon occurred at around 10.30 am after the city was lashed by a morning downpour. Several citizens in various parts of the city, including Salt Lake, enjoyed the sight of a perfect rainbow ring with a circle in red at the inner side and yellow on the outer spectrum.
As informed by the experts, the circle around the Sun is an atmospheric optical phenomenon. The phenomenon includes a halo with a radius of approximately 22 degrees in the sky. The phenomenon popularly known as the 22 degree circular halo of the sun or occasionally occurs during pre monsoon or monsoon period. As explained by scientists, generally these kinds of cirrus clouds get formed when water vapour freezes into ice crystals at altitudes five to ten kilometres above the earth’s surface.
According to the former director of the Research and Academic wing of the M P Birla Institute of Fundamental Research, M P Birla Planetarium in Kolkata, Debiprosad Duari, the phenomenon occurs when sunlight passes through low-lying water crystal bearing clouds. “Sun rays get refracted by an amount of 22 degrees because of the hexagonal shape of the water crystals,” explained Mr Duari. “The frequency of such events is comparatively more during the rainy season on cloudy days. The 22 degree halos appear when the sky is covered by thin cirrus or cirrostratus clouds that often come a few days before a large storm front,” he added.
As underlined by the former director, the atmospheric optical takes place once or twice in the city and is a regular occurrence in Kolkata.
The same process also occurs around the moon. In that case, the phenomenon is called the moon ring or winter halo.