Asaph Hall III (October 15, 1829 – November 22, 1907) was an American astronomer who is most famous for having discovered the moons of Mars (namely Deimos and Phobos) in 1877. He determined the orbits of satellites of other planets and of double stars, the rotation of Saturn, and the mass of Mars.

Hall was born in Goshen, Connecticut, the son of Asaph Hall II (1800-42), a clockmaker, and Hannah Palmer (1804-80). His grandfather Asaph Hall I was a Revolutionary War officer and Connecticut state legislator. His father died when he was 13, leaving the family in financial difficulty, so Asaph left school at 16 to become an apprentice to a carpenter. He later enrolled at the Central College in McGrawville, New York, where he studied mathematics. There he took classes from an instructor of geometry and German, Angeline Stickney. In 1856 they married.

In 1856, he took a job at the Harvard College Observatory in Cambridge, Massachusetts, and turned out to be an expert computer of orbits. Hall became assistant astronomer at the US Naval Observatory in Washington DC in 1862, and within a year of his arrival he was made professor.