On the night of August 17, 1877, at the U.S. Naval Observatory in Washington, D.C., an astronomer named Asaph Hall was ready to give up. Days of fog rolling off the nearby Potomac had repeatedly ruined his search for a hypothetical moon of Mars, and the frustration was wearing him down. His wife wouldn’t let him quit. That same night, he found not one Martian moon, but two.
A Planet That Wasn’t Supposed to Have Any Moons
For centuries, astronomers had simply assumed Mars had no moons at all, nobody had ever spotted one. In August 1877, Mars reached an unusually close opposition to Earth, appearing larger and brighter than usual, giving Hall a rare window to search seriously. He had access to the observatory’s 26-inch refractor, then the largest telescope on Earth, and he used it to hunt for faint objects lost in the glare right next to the planet.
On August 11, he caught something, a faint point of light near Mars. Then the fog rolled in. Foggy Bottom, the Naval Observatory’s own neighborhood, earned its name honestly, and the weather kept Hall from confirming anything for nearly a week.
The Wife Who Wouldn’t Let Him Quit
Here’s the part of the story that rarely makes it into the astronomy books. Hall’s wife, Angeline Stickney Hall, was a mathematician in her own right, sharp enough that as his geometry instructor years earlier, Hall and his classmates had made a running game of trying to stump her and never once succeeded. She’d given up her own academic career after marrying him, as women of the era typically had to, but she never stopped doing the math behind the scenes of his research.
When the fog and repeated failures nearly convinced Hall to abandon the search entirely, it was Angeline who pushed him to keep going. He went back out on August 17, confirmed the object he’d lost days earlier, a moon later named Deimos. Then, while waiting that same night to catch another glimpse of it, he spotted something else entirely, a second, closer moon. He’d found Phobos too. The Naval Observatory’s superintendent announced both discoveries to the world the very next day.
A Name Written Permanently Onto the Moon Itself
Nearly a century later, in 1973, the International Astronomical Union named the largest crater on Phobos in Angeline’s honor: Stickney, after her maiden name. It’s not a small tribute either, the crater stretches almost 6 miles across, consuming close to half of the entire moon’s surface, the result of an impact so violent it nearly shattered Phobos completely. If you’re curious about the strange, doomed little moon Hall found that night, our full profile of Mars’s size, distance, and orbit covers Phobos and Deimos in more detail, including the moon’s slow, inevitable collision course with the planet it orbits.
Predicted in Fiction 150 Years Early
One more strange footnote belongs in this story. In 1726, satirist Jonathan Swift published Gulliver’s Travels, in which fictional astronomers claim to have already discovered two moons orbiting Mars, describing their orbital periods with genuinely uncanny accuracy, more than 150 years before Hall actually found them. Nobody knows exactly why Swift guessed so specifically. What’s certain is that on one frustrating, foggy week in Washington, a real husband-and-wife team turned that old fictional guess into fact, and left her name permanently written across the surface of the moon he almost gave up looking for.
For more on the discovery, check out the historical account from Astronomy.com and the detailed retrospective from Space.com.
Stickney crater, the largest feature on Phobos, spans nearly half the moon’s diameter. It’s named for Chloe Angeline Stickney Hall, the mathematician whose encouragement kept her husband searching. (Image: NASA/JPL-Caltech/University of Arizona)