Mars came unusually close to Earth in 1877, and Hall used the opportunity to search for Martian satellites with the Naval Observatory's 26-inch refractor, then the largest in the world. The search was discouraging, and Hall later wrote that he might have given up had it not been for the encouragement of his wife, Angeline Stickney. In the early hours of August 12 he found a faint point of light near the planet: Deimos. Days later he found the inner moon, Phobos.
Astronomers had speculated about Martian moons for centuries, and Jonathan Swift had even given Mars two satellites in Gulliver's Travels in 1726. None had ever been seen. Hall found both within a week during the favourable opposition that August, Phobos following on August 18.
Deimos turned out to be tiny: a lumpy body with a mean radius of about 6.2 kilometres, orbiting 23,460 kilometres from Mars, much farther out than Phobos, once every 30.3 hours. Hall had been in charge of the 26-inch telescope since 1875, and it proved just powerful enough to catch both moons. The names were suggested by Henry Madan, a science master at Eton College, after figures from Greek myth who attend Ares, the god of war: Phobos, fear, and Deimos, dread.
His wife was remembered too. The largest crater on Phobos is named Stickney, after the woman whose persistence, by Hall's own account, kept the search going.
Key people: Asaph Hall, Angeline Stickney