Halo: A Optical Phenomenon

Halos are most often seen in the sky. Recently we have noticed one at 28th may 2020. All of us now are describing it with a different meaning from different thoughts. But exactly what it is and what it mean?

Come lets know about the phenomenon.

Halo is a originally a greek word. First used by Aristotle, Halo is a circular coloured ring formed in the sky or in earth’s atmosphere.

It is and optical Phenomenon formed due to light by either sun or moon, it is formed around any celestial body. Halos are produced due to the crystal present in the atmosphere. Halos are of different forms, they may be coloured rings, white rings, archs or patches in the sky. Generally this are formed around the sun or moon. Or even they may appear anywhere in the sky opposite to the light sources. There are many forms like the most common 22° halo or also named as circular halo. There are more such as light pillars, sundogs but these halos are extremely rare.

In the upper troposphere (6km-10km) the cirrus or the cirrostratus clouds are present. The crystal responsible for the halo are suspended in the cirrus clouds. Sometimes during the cold weather the particles also float above the ground, in such situations these crystal are known as diamond dust.

The orientation of the dust particles are responsible for the shape of the halo formed. Lights are reflected and refracted inside the crystal and they may split due to dispersion. The crystals behaves as prism and mirrors, refracting and reflecting rays on their faces, sending shaft of light in particular directions.

In the earliest days before meteorology was developed, the halos are used a phenomenon to determine the weather forecast. The places where the halo is seen have probable chances of rain fall in the next 24hours. They indicate the cirrus clouds that cirrostratus clouds that cause them can signify an approaching frontal system. Among all the best known halos is the 22° halo or the circular halo. These are formed around the sun or moon roughly with a radius of 22°. The crystals are suspended semi-randomly in the atmosphere. No light is reflected towards the inside of the ring leaving the area dark than the rest sky outside the ring. It seems to be a dark hole in the sky.

Most often people confuse these halos with corona, corona is a different optical Phenomenon which is formed due to droplets rather than crystal. These phenomenon results in a multicolored disk rather than a circle.

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