Rainbow around the sun

Today in South Africa we have a rainbow around the sun

22 degree halo

A 22° halo is a halo, one type of optical phenomenon, forming a circle 22° around the sun, or occasionally the moon. It forms as sunlight is refracted in hexagonal ice crystals suspended in the atmosphere. As the light beam passes through two sides of the prism forming a 60° angle, the angle of minimum deviation is almost 22° (namely, 21.84° on average; 21.54° for red and 22.37° for blue). This wavelength-dependent variation in refraction causes the inner edge of the circle to be reddish while the outer edge is bluish. A 22° halo may be visible on as many as 100 days per year.

Pathway of light through a hexagonal prism in the optimal angle resulting in minimum deviation.

A 22° halo photographed in Johannesburg, South Africa

Light passing through the hexagonal ice prisms is deflected twice, which produces deviation angles ranging from 22° to 50°. Lesser deviation results in a brighter halo along the inner edge of the circle, while greater deviation contribute to the weaker outer part of the halo. As no light is refracted at smaller angles than 22° the sky is darker inside the halo.

22° halos form when the sky contains millions of variously oriented (poorly correlated) ice crystals. Some of these happen to be aligned perpendicular to the sun’s light as viewed by any given observer, which produces the illuminated 22° circle, while other crystals produce the same phenomenon for other observers.

Like other ice halos, 22° halos appear when the sky is covered by thin cirrus clouds containing the ice crystals that cause the phenomenon. Small colourful coronas much nearer the sun produced by water droplets can occasionally be confused with 22° halos.

Info from Wikipedia

Photo by my little sister in Johannesburg – thank you

2 thoughts on “Rainbow around the sun

  1. That is beautiful! Have never seen that here. We did see a similiar phenomenon with the moon one night years ago but never with the sun. Beautiful!


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