Discovery of Phobos

Date: August 18, 1877 • Location: Washington, United States

American astronomer Asaph Hall discovered Phobos, the larger of Mars's two moons, six days after discovering Deimos, the smaller one.

Asaph Hall III was an American astronomer who is best known for having discovered the two moons of Mars, 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.