Have you ever seen what looks like a rainbow encircling the sun?
A coloured sun halo spotted by Derek in Ryton, Gateshead on 11 August.
This weather phenomenon is known as a halo, which usually occurs around the sun. Moon halos have also been observed, though these are relatively rare.
Halos are caused by ice crystals in the air that are usually associated with high-altitude cirrus cloud. These crystals reflect sunlight, normally producing a white halo. However, when the sun's rays strike the crystal at a particular angle some light may be refracted. This causes the halo to be rainbow coloured, like in the example above.
The size and shape of a halo can also be altered by the angle at which the crystal refracts light. In some instances, the angle of the ice crystal causes only parts of the halo to form, creating what we know as a circumzenithal arc.
A small circumzenithal arc caught on camera by Weather Watcher The Wild Garden on 3 July in Sheffield.
Before modern day meteorology was invented, sun halos were used to forecast rain, as the cirrus cloud with which they are associated can signify an approaching frontal system. Yet, with the possibility of weather fronts being idle or even changing path, today's weather forecasts tend to use a more sophisticated system of computer models rather than sun halo observation.
An example of a coloured sun halo. This photo was taken near Bamburgh, Northumberland.
Keep submitting your photos of halos and arcs to the Weather Watchers site. Don't forget, though, that looking directly at the sun could damage your eyesight, so next time you spot a halo remember to shield your eyes while observing.
