comet

Small icy body that partially evaporates as it approaches the Sun; made up of a head with a solid core and tails composed of gas and dust.

coma

Cloud of gas and dust particles emitted by the expulsion of gas from the nucleus when a comet approaches the Sun.

nucleus

Central part of the comet; composed mainly of ice and rocky matter.

head

Part made up of the nucleus and the coma.

dust tail

Visible tail formed by dust particles pushed out of the coma by pressure from the Sun’s rays; can reach over 6 million mi in length.

ion tail

Almost invisible tail formed by the gas of the coma pushed back by the solar wind; can reach several hundreds of millions of miles in length.