Astronomer Fred Whipple created the term "dirty snowballs" as a description of comets. These bodies are made of dust, rocks, organic compounds, and ice. Ice, in the form of dry ice, water ice, and various frozen gases, makes up most of the comet. Comets have three parts: nucleus
, and tail.Size:
A comet nucleus can range in size from less than a mile (1 kilometer) to 15 miles (25 km) across. The longest comet tail, which measured over 354 million miles (570 million kilometers), belonged to Comet Hyakutake in May 1996.