Halley's Comet is a periodic comet that can be seen from Earth every 75-76 years. It was first recorded in 239 BC and was named after the British astronomer Edmond Halley, who predicted its return in 1758. The comet is composed of ice, dust, and rock, and its nucleus is estimated to be about 15 kilometers in diameter. When the comet passes close to the Sun, it releases gas and dust that form a bright tail. Halley's Comet last appeared in 1986 and is expected to return in 2061.