Coimbatore residents were surprised by a rainbow halo that formed around the sun sometime around 9.30 a.m. on Friday. The surprise turned into curiosity when the phenomenon intensified and the halo became very prominent in the seven colours of the rainbow.

Coimbatore has witnessed a similar halo in 2005. Terming it a normal phenomenon, D. Mangalaraj, Head, Department of Nano-Science and Nano-Technology, Bharathiar University, said such a halo is formed when water droplets that accumulate around the sun evaporate. When there is differential moisture content in the atmosphere surrounding the sun, evaporation takes place and because of the proximity of the sun, the white of the water is scattered into seven colours and hence the rainbow effect.

The intensity reduced after almost three hours and the halo faded away.

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