Our Solar System contains the Sun, the eight planets, as well as numerous dwarf planets, many asteroids, and an unknown number of comets. Comets have often featured in historical accounts as portents of doom or disaster (one features in the Bayeux Tapestry, for example), but the reality is that they are giant dirty snowballs. As they get close to the Sun they begin to warm, and some of the ice begins to turn to gas, creating the spectacular tails visible from Earth. This activity helps students to understand what comets are made of, and why they look the way they do in the sky.