August 17, 2022
On this date in 1877, American astronomer Asaph Hall discovered one of the two moons of Mars, which he named Phobos. In mythology, Phobos is one of the sons of Ares, the Greek counterpart to the Roman god of war, Mars. Only five days prior, on August 12, 1877, Hall had discovered the Martian moon Deimos, also named for a son of Ares. Phobos and Deimos remain the only two Martian moons discovered.
The image on the left shows American astronomer Asaph Hall at the United States Naval Observatory in 1899. Hall is best known for his discovery of the two moons of Mars in August 1877. On the right is an image of the Martian moon Phobos taken by the Mars Reconnaissance Orbiter in March 2008. Image credit left: U.S. Navy, right: NASA/JPL-Caltech/University of Arizona