List the four main parts of a comet, and identify their physical characteristics?

The 4 main parts to a coment are
1. Head- Nebulous envelope around the coment
2. Nucleus- Central portion of the head of a comet. Solid part of the comet that has holes filled with ices like water, carbon dioxide (dry ice), and carbon monoxide. 
3.Coma- A cloud which is the atmosphere of the comet and can extend for millions of miles.
4.Tail- Dust Particles that trail behind