Matt Craig, MSUM Department of Physics & Astronomy, will talk about “Upside-down Rainbows, Sun Dogs and Halos: Optical Phenomenon Caused by Ice Crystals” at a free seminar Friday, January 21 from 2:30-3:20 p.m. in Hagen Hall room 325.

Ice crystals in the atmosphere cause a much wider variety of optical effects than water droplets. Water droplets cause rainbows, but ice crystals cause sun dogs (bright images of the sun 22 degrees to either side of it), halos, and oddly shaped arcs. One of those is the circumzenithal halo, an upside-down “rainbow” just as brilliantly colorful as a regular rainbow. On November 23, 2010, there was a spectacular display of several halos and arcs; this talk will attempt to explain the cause of each of the features observed that day.