Comets are occasional visitors from the icy reaches of the outer Solar System. This lecture discusses the orbits, structure, and properties of comets, and introduces the "dirty snowball" model of a comet nucleus. The end of class was a demo where I created a model of a comet nucleus from common household and office materials. Imagine a twisted combination of Alton Brown and Emeril Lagasse with a PhD in Astrophysics and you get the idea. We were not able to arrange for a videographer to come, but we did get some stills before the batteries died on the digital camera. The pictures are on the lecture webpage. The lecture is slightly abbreviated because we did the student evaluation of instruction surveys before class started. Recorded 2006 Nov 29 in 100 Stillman Hall on the Columbus campus of The Ohio State University.