The Hindu : National : Solar ring observed

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Tuesday, Jul 06, 2010
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National

Solar ring observed

Ananya Dutta

KOLKATA: As the streets in the city bore a deserted look owing to the nationwide strike in protest of the fuel price hike, the skies offered an unusual spectacle on Monday as a halo formed around the sun under the influence of an unusual atmospheric phenomenon.

The ring observed around the sun, which lasted for nearly an hour starting at 10:30 a.m., is a phenomenon described as the “22 degree halo of the Sun.” It occurs because of the presence of a certain kind of cloud called “cirrus clouds,” D. P. Duari, Director (academic and research) of the Birla Planetarium, said here.

“Cirrus clouds are formed when water vapour freezes into ice crystals about five to 10 km above the earth's surface. The ice crystals formed in these clouds often take the shape of hexagonal crystals and sunlight passing through these crystals is refracted at a 22 degree angle, creating a ring-like shape around the Sun,” he said.

However, the phenomenon is usually observed in a localised area because these clouds — characterised by thin, wisplike strands, often accompanied by tufts — have to be extensive, forming a sheet of cirrus called cirrostratus, Dr. Duari said.

The timing of the celestial delight, when last observed in West Bengal in 2008, sparked fears about the apocalypse.

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