BBC – If you had your eyes to the sky this week, you may have seen or even photographed halos or circles of light around the sun.
This happens when we have a thin layer of cirrus cloud moving across the sky. Cirrus is very high cloud made up of ice crystals. (Continue reading below video)
Sometimes the cirrus is so thin we are not aware of any cloud in the sky. However as it passes in front of the sun, refraction of the light by the ice crystals causes the halo to form.
We can also sometimes see the same effect when it’s a clear night with a full oon and the thin layer of cirrus moves across the moonlit sky.