Asaph Hall III (October 15, 1829 - November 22, 1907) was an American astronomer. In 1856, Hall 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. In 1875 Hall was given responsibility for the USNO 26 inch telescope, the largest refracting telescope in the world at the time. It was with this telescope that he discovered Phobos and Deimos in August 1877. Hall also investigated stellar parallaxes and the positions of the stars in the Pleiades star cluster. He retired from the Navy in 1891. He became a lecturer in celestial mechanics at Harvard University in 1896, and continued to teach there until 1901. He died in 1907 at the age of 78. The Hall crater on the Moon, Hall crater on the Martian moon Phobos and Asteroid 3299 Hall are named in his honor.