Dr. Dennis Schatz created the first "Earth-based" comet many years ago. His very popular demonstration is conducted in classrooms and science museums around the world. You can build a comet following Schatz's very own recipe, "Making a Comet in the Classroom." http://www.noao.edu/education/crecipe.html The ingredients are simple: water, frozen carbon dioxide (dry ice), dust and dirt, ammonia, and a dash of organics. Over a few hours time the resulting cometary nucleus will melt and break apart much like a genuine comet does as it approaches the Sun.

Schatz is the Associate Director for Educational Programs at the Pacific Science Center in Seattle, Washington, where he continues to write, teach, and create great science lessons for children and adults.