Atmospheric Optics Home     60 and 90° prisms Previous Feature Next Feature Subscribe to Features on RSS Feed

Infralateral Arc imaged at Otway Massif, Grosvenor Mountains, Antarctica by Monika Kress. ©Monika Kress, shown with permission.

Circling the sun at top right is the familiar 22° halo and slightly beyond it is a bright sundog. These halos are produced by sun rays passing between ice crystal faces tilted 60° to one another. The 60° prism splits the light into colours.

Why are the colours of the arc at lower left spread more widely?    This is a rare infralateral arc. It is produced by rays passing between crystal facets angled 90° to each other. The wider prism strongly refracts and splits the light.