Tonight in 1877, at the U.S. Naval Observatory in Washington, Asaph Hall found a second moon of Mars. He had found the first, Deimos, six nights earlier, after very nearly giving up — his wife, Angeline Stickney Hall, had talked him into one more night at the eyepiece. The telescope was the 26-inch Clark refractor, then the largest in the world; Mars was about as close as it ever comes; and the two moons are tiny, so tiny that every earlier search had looked straight past them.
Phobos is the inner one: about 22 km across, a lumpy potato orbiting roughly 6,000 km above the Martian surface — closer to its planet than any other moon we know. It goes round in 7 hours 39 minutes, faster than Mars turns, so from the ground it rises in the west and sets in the east, twice a day. It is also slowly spiralling in. In a few tens of millions of years it will break up and briefly give Mars a ring. I find that oddly cheering.
The biggest crater on Phobos is named Stickney. Good.
Here’s the clever bit about that telescope: Alvan Clark and his sons ground the 26-inch objective in their workshop across the river from Boston, and the Navy put up a dome to hold it. First light was November 1873. Four years later it was finding moons. Unglamorous credit, then, to the men who figured the glass one slow stroke at a time.
Hall left school at thirteen to apprentice as a carpenter and was finding moons at forty-seven. Late bloomers, take note — the league keeps no age limit on discoveries.