Australian Weather Calendar: September 2017

September photograph by Kylie Gee

Kylie Gee saw a Facebook post one evening about a moon halo visible over Perth, and drove out to her favourite location near Bencubbin to photograph it.

Halos form when the moon or sun shines through cirrus or cirrostratus clouds. These wispy clouds, high in the atmosphere, are made of ice crystals. A halo is formed in a similar way to a rainbow: As light passes through the ice crystals its path is refracted, or bent. The angle of refraction varies from 22° to 50°, and no light is refracted at less than 22°. As a result, the observer sees a halo around the light source.

Diagram