A comet's nucleus is primarily composed of ice and gas, such as water ice, carbon monoxide, and methane.

A comet's tail is composed of dust and gas that are released from the nucleus as the comet approaches the Sun and is heated.

The primary difference between a comet and an asteroid is that comets have tails, while asteroids do not. Comets also tend to be made of ice and gas, while asteroids are made of rock and metal.

Halley's Comet is the most famous comet because it is visible from Earth every 76 years. It was first observed in 240 BC and has been seen many times since then.

The largest comet ever observed is Bernardinelli-Bernstein, which was discovered in 2021. It has a nucleus that is about 120 kilometers in diameter, which is larger than the state of Rhode Island.

If a comet passes too close to the Sun, it can be destroyed by the Sun's heat. The comet's nucleus can vaporize, and the tail can be blown away by the solar wind.

The Rosetta spacecraft was the first spacecraft to land on a comet. It landed on Comet 67P/Churyumov-Gerasimenko in 2014 and studied the comet for over two years.

Shoemaker-Levy 9 was a comet that collided with Jupiter in 1994. It was the first time that astronomers had ever observed a comet colliding with a planet.

Comet Leonard is expected to pass close to Earth in 2023. It is expected to be visible to the naked eye for several months.

Comet Borisov was discovered in 2020 and is expected to pass close to Earth in 2031. It is the first known interstellar comet, meaning that it originated from outside of the Solar System.

Comet PanSTARRS was discovered in 2021 and is expected to pass close to Earth in 2029. It is expected to be visible to the naked eye for several months.

Comet K2 was discovered in 2022 and is expected to pass close to Earth in 2030. It is expected to be visible to the naked eye for several months.

Comet C/2023 E3 was discovered in 2023 and is expected to pass close to Earth in 2032. It is expected to be visible to the naked eye for several months.

Comet C/2024 F3 was discovered in 2024 and is expected to pass close to Earth in 2033. It is expected to be visible to the naked eye for several months.

Comet C/2025 G2 was discovered in 2025 and is expected to pass close to Earth in 2034. It is expected to be visible to the naked eye for several months.