Physics Photo of the Week – Warren Wilson College

February 6, 2004

Photo by Donald Collins

Ice Halo around the sun. This photograph was taken from in front of Spidel (notice the pointed cupula and the roof line) at about 1:00 pm on Wednesday, Feb. 4, 2004. The sun is obscured by the lamppost. The halo is caused by refraction of sunlight by ice-crystals in the cirrus clouds at high elevation. This effect is fairly common and is often seen in association with the moon as well. The ice-crystal cirrus clouds that produce the effect represents the influx of warm, moist air from the tropics and sub-tropics moving over top of the cold, polar airmass. The cirrus clouds usually predict wet or snowy weather the following day. The rain began late afternoon the next day after this photo.

Here are some links to further explanation of the ice halo:

http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/opt/ice/halo/22.rxml

http://www.sundog.clara.co.uk/halo/halosim.htm

Rainbows, halos, and glories by Robert Greenler, Cambridge University Press, 1980 (Martha Ellison Library)

Donald F. Collins

Anyone who has a photograph of an interesting physics or other natural phenomonon is welcome to send the photo to Don Collins for possible display in this weekly series.