What did Edmond Halley discover?

Edmond Halley is known for calculating the orbit of the comet that was later named after him, Halley's comet. He was an English astronomer and mathematician.

Halley first worked as an assistant to John Flamsteed, the astronomer royal at Greenwich Observatory in 1675. He published his star catalogue of the Southern Hemisphere in 1678. In 1705, he published "A Synopsis of the Astronomy of Comets," in which he mapped the orbit of Halley's comet. He became astronomer royal in 1720. Halley was born in 1656 in Haggerston, London and studied at the University of Oxford. He died in 1742 at the age of 85.