Halley's Comet is a periodic comet that is visible from Earth every 75-76 years. It was named after English astronomer Edmond Halley, who observed it in 1682 and calculated its orbit. The comet is composed of ice, dust, and rocky material, and its nucleus is estimated to be between 10 and 16 kilometers in diameter. When the comet approaches the Sun, it produces a spectacular tail of gas and dust that can stretch for millions of kilometers. It last appeared in the inner Solar System in 1986 and will return again in 2061.