Halley's Comet is a periodic comet that can be seen from Earth every 75-76 years. It is one of the most famous comets in the Solar System, and its most recent appearance was in 1986. The comet is named after Edmond Halley, who was the first to predict its return. Halley's Comet has been observed since ancient times and is believed to have been seen by Chinese astronomers in 240 BC. It is composed of ice, dust, and rock, and its nucleus is estimated to have a diameter of about 15 kilometers (9 miles). When it passes close to the Sun, it releases gas and dust that form its characteristic tail.