Anatomy of a Comet
Hi-Res JPEG (134 KB)
A comet is commonly described as having 3 parts:
Nucleus - the dark dirty snowball composed of ice, dirt, rock and gas
Coma - the halo of gas, ice and rock bursting forth from the nucleus
Tail - in this case, both the dust and ion tail
More:
CREDIT: NASA/JPL-Caltech/UMD.