Asaph Hall
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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.
Hall at the USNO in 1899
Hall's former home in the Georgetown neighborhood of Washington, D.C., after enlargement. Note Angeline on front steps and two workers.
Hall's Gold Medal of the Royal Astronomical Society
Deimos (moon)
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Deimos is the smaller and outer of the two natural satellites of Mars, the other being Phobos. Deimos has a mean radius of 6.2 km (3.9 mi) and takes 30.3 hours to orbit Mars. Deimos is 23,460 km (14,580 mi) from Mars, much farther than Mars's other moon, Phobos. It is named after Deimos, the Ancient Greek god and personification of dread and terror.
Deimos, captured by the Mars Reconnaissance Orbiter in enhanced color
Asaph Hall III, discoverer of Deimos
Deimos transits the Sun – as viewed by the Mars rover Opportunity (4 March 2004)
Deimos and Phobos as seen from Mars, compared to the Moon as seen from Earth (in angular sizes)