What is sun halo?

Source: By The Times of India

India's tech hub witnessed an optical phenomenon - Sun Halo or a rainbow-coloured ring around the sun across Bengaluru on 24 May 2021, which brightened up the day with several people on social media sharing pictures and funny captions with it.

Bengaluru residents were left awed by the rainbow-coloured halo surrounding the sun as the striking circular rainbow ring was reportedly visible from most parts of the capital of Karnataka.

It was first seen around 11 a.m. and lasted for over an hour, in which time Bengaluru resident’s flooded social media with pixtures of the rare phenomenon.

What is a Sun halo?

Sun halo, also known as '22 degree halo', is an optical phenomenon that occurs due to sunlight refracting in millions of hexagonal ice crystals suspended in the atmosphere. It takes the form of a ring with a radius of approximately 22 degrees around the sun or the moon.

Where the halos are formed?

Circular halos specifically are produced by cirrus clouds, which are thin, detached, hair-like clouds. These clouds are formed very high up in the atmosphere, at a height of over 20,000 feet.

What causes a sun halo to appear?

The halo phenomena happen when the light is reflected and refracted by ice crystals and may split into colours because of dispersion, according to the UK based Atmospheric Optics, a knowledge-sharing website. It further explained that the crystals behave like prisms and mirrors, refracting and reflecting light between their faces, sending shafts of light in particular directions. Atmospheric optical phenomena like halos were used as part of weather lore, which was an empirical means of weather forecasting before meteorology was developed. They often indicate that rain will fall within the next 24 hours, since the cirrostratus clouds that cause them can signify an approaching frontal system.

How can one view a halo?

Just like a rainbow, a halo is visible when viewed from the right angle - sometimes appearing just white but often with colours of the spectrum also clearly present. They are the collective glints of millions of crystals that happen to have the right orientation and angular position to direct their refracted light into your eye.

How often do sun halos occur?

Such Sun or Moon halos are not so common. However they have been witnessed earlier in the country in the past. Such a halo could occur around the moon at night, which is formed due to the same phenomenon.