Yesterday there was a very clear ice halo above Rhodes University. I was busy working in the Geography Department when just after 9.00 Ian Meiklejohn called me out of the office to come and look. After a quick glance I dashed back in for my trusty Samsung Duos phone to grab a few pictures of the halo silhouetted against the clock tower before it disappeared.
I think this is one of the most common halos. It was gone quite quickly but more of them appeared later in the morning as bands of high cirrus clouds continued to come by.
These 22 degree halos are formed when the sun’s rays pass through millions of hexagonal ice crystals high up in cirrus clouds. You can see the clouds streaming across the photos carried by yesterday’s hot northerly winds. When the light passes through two sides of the hexagonal crystals then its angle is changed to 22 degrees or more, so you see a sharp halo – usually with the red inner band which is visible in my pictures. There’s a nice explanation at the Atmospheric Optics website.