A comet is a cosmic snowball made of frozen gases, rock, and dust that orbits the Sun. Comets are believed to be remnants from the formation of the solar system about 4.6 billion years ago. They are typically the size of a small town when frozen. When a comets orbit brings it close to the Sun, it heats up and spews dust and gases into a giant glowing head larger than most planets. The dust and gases form a tail that stretches away from the Sun for millions of miles.

Comets are primarily made up of a nucleus, coma, hydrogen envelope, dust, and plasma tails. The gravity of a planet or star can pull comets from their homes in the Kuiper Belt or Oort Cloud, redirecting them towards the Sun. When a comet gets close to the Sun, it starts heating up, and eventually, the ice begins to turn to gas. This can cause jets of gas to burst out of the comet, bringing dust with it. The gas and dust create a huge, fuzzy cloud around the nucleus called the coma. As dust and gases stream away from the nucleus, sunlight and particles coming from the Sun push them into a bright tail that stretches behind the comet for millions of miles. When astronomers look closely, they find that comets actually have two separate tails. One looks white and is made of dust. This dust tail traces a broad, gently curving path behind the comet. The other tail is bluish and is made up of electrically charged gas molecules, or ions. The ion tail always points away from the Sun.

Comets leave a trail of debris behind them that can lead to meteor showers on Earth. For instance, the Perseid meteor shower occurs every year between August 9 and 13 when Earth passes through the orbit of Comet Swift-Tuttle. While some comets can be seen with the naked eye when they pass close to the Sun, most are too small or too faint to be seen without a telescope.