Comets Becky Bray & Patrick Meyer 01.27.01 Comets often are described as "dirty snowballs" because they are made of frozen lumps of gas and rock. They have highly elliptical orbits which cause them to spend most of their time frozen in space in the outer solar system or farther. At these distances, comets are hardly visible except by the reflection of sun light. It is when comets approach the sun that they become visible and show the grand tails that we associate with them. When they approach the Sun, the intense radiation from the sun converts some of the ice into ionized gases. The solar wind and magnetic fields between the planets force the ionized gases to stream from the comet forming the tail. The tail, however, does not fall directly behind the comets path, it flows directly away from the sun (see illustration above. ©2001 NASAkids.com , Science@NASA  Becky Bray & Patrick Meyer ©2001 The Aurora Collection, Inc. All Rights Reserved. Site Development by: Interactive Multimedia. Inc.