Final answer:
A comet is a small body that, when approaching the Sun, heats up causing its icy nucleus to vaporize and form a coma and tail. These features are more visible when the comet is closer to the Sun. Comets have two types of tails: dust and ion, with the dust tail usually being more visible.
Step-by-step explanation:
A comet is produced by a lump of rock and ice usually between 1-100 km in diameter. In long, elliptical orbits, the icy nucleus stays frozen until nearing the Sun. That's when some of the ice vaporizes and releases dust and gas that is blown away to form a coma and tail.
The appearance of comets is not always spectacular, resembling a faint, diffuse spot of light in our night sky. However, as a comet approaches the Sun, it heats up, and substances such as H₂O vaporize and release dust. The dust and gases liberated escape into space, forming an atmosphere around the comet's nucleus and contributing to the development of a tail.
Today, comets are admired for their beauty when they come close enough to put on a good sky show. The tails of comets can be divided into two types: a dust tail, and a gas or ion tail, both of which are visible as the comet nears the Sun. Understanding the nature of comets helps us appreciate these hairy stars and their spectacular appearances in the night sky.