The past is a foreign country indeed.

Finding the missing world required maths — very complex maths, and that's where Williams and other mathematicians came on the scene. Before the invention of calculators, so-called human computers — often women, since it was unglamorous work — did all the complex math that astronomers required, by hand. For Lowell's research, Williams calculated where he should look for how large of a missing object, all based on the discrepancies in the orbits of Neptune and Uranus.

Lowell never spotted Pluto, and the quest languished for a few years before Tombaugh picked up the work. And then, there it was: In 1930, those calculations paid off when Tombaugh caught sight of an object moving through the solar system. "There's a specific result that came of her calculations, so that's pretty exciting," Clark said.

But Williams wasn't there to see it, Clark said. In 1922, Williams had married and Lowell's widow had fired her because she felt it inappropriate to employ a married woman. The pair took jobs at a Harvard observatory in Jamaica. In 1935, Williams was widowed herself and moved to New Hampshire, where she died in poverty.