Typical 22 degree Haloes

The typical appearance of a 22 degree halo in the cirrus ahead of an approaching cold front.

The colours are clearly visible but are not as well defined as in a rainbow. Even when the sun itself is blocked out the glare from the cirrus can be very strong, so eye protection is often needed.

The smooth cirrus background made this strong halo stand out. It shows very well how the brightness drops off gradually outside the halo. The brightness falls off very rapidly at the inner edge where the sky is darker than outside the halo.

On a showery afternoon I was expecting to see rainbows rather than haloes. This good 22 degree halo was visible in a large gap between showers. An hour later it was raining again.

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