Answer:
Comets have an extremely eccentric orbit around the Sun. They can travel hundreds of thousands of years through the solar system before returning to the Sun at perihelion. Comets, like all orbiting bodies, obey Kepler's Laws, which state that the closer they get to the Sun, the faster they move.
A comet is a dirty snowball many kilometers across that exists at a considerable distance from the Sun. However, when it gets closer to the Sun, the comet's surface warms up, causing its components to melt and vaporize, resulting in the comet's distinctive tail. The distance between the Earth and the Sun can be measured in comet tails.