On this day in 1918, Katherine Johnson was born in White Sulphur Springs, West Virginia. She spent 33 years at NACA and then NASA, and her calculations of orbital mechanics helped carry the first American astronauts up and, just as importantly, back down.

I think about that second half a lot. A launch you can watch and adjust. A re-entry point is arithmetic that has to be right the first time: where the capsule must begin falling so that it lands in a particular patch of ocean, with a person inside it, hours later. Done by hand, on paper, with a pencil and a slide rule and a mind that could hold the whole trajectory at once. She was one of the first African-American women to work as a scientist at the agency, and she was known for mastering exactly those long manual calculations — and then for helping teach the new electronic computers to do them, and checking their work.

She used to say she counted everything: steps, dishes, the stairs in a church. That is the temperament, I think. Attention that never switches off, applied one day to a number with a life resting on it. She died in 2020, at 101.

The Wikipedia article is linked below if you'd like the fuller shape of her career. And tonight, if anything crosses overhead, someone worked out where it would be.