There are so many precocious geniuses out there. So many people have achieved great things because they worked on them since the first grade. That's fine for them, but precocity is annoying. Let’s talk about the woman who made an incredible discovery via a few post-graduate courses and volunteer work.


Henrietta Swan Leavitt made a discovery that let us figure out the size of the universe. She so extensively classified variable stars that, during her time, she was responsible for half of the known variable stars logged in astronomy. And this all started when she realized, during her senior year in college, that she hadn’t studied what she wanted to study.

During Leavitt’s last year at Radcliffe, she took an astronomy course, and enjoyed it more than the subjects she had studied for the past few years. Some might respond to this by moping. Leavitt responded by taking a quick course after college before being knocked down by illness that left her nearly deaf. Deciding that she wasn’t going let a brush with death dissuade her from a course of study in which she’d earned an encouraging A-, she looked for other ways to pursue astronomy.


Pretty soon, she found that Harvard was looking for astronomy helpers. As telescopes and cameras improved, astronomical institutions had an in-rush of data to analyze. They did this with computers. Not the machines, though — "computer,” was the term used for either non-paid or low-paid workers who did the detail-oriented yet repetitive work that electronic computers do today. Leavitt started volunteering, and in only seven short years she had worked her way to a paid position – still as a computer. She used a piece of cutting-edge technology, known back then as a blink comparator. It flipped rapidly back and forth between two images, allowing the viewer to see the difference. Leavitt was looking for variable stars.

Variable stars were stars that increased and decreased in brightness over time. Leavitt catalogued about 2,400 – half the known variable stars at the time. Perhaps it’s no surprise that, after watching these stars flicker back and forth in tens of thousands of blink comparator images, Leavitt got to wondering about them. Perhaps, she thought, the period over which they brightened and darkened had some relation to their intrinsic brightness. She was briefly stymied by the fact that no one knew the distance to any of these variable stars – known as cepheids. By targeting the cepheids in one cluster, the Magellanic Cloud, she figured that she’d get variables from roughly the same distance. By comparing them, she discovered that the longer the period of the variation, the more intrinsically bright the star was.

This provided the stepping stone to finding out not just the distance to other stars, but the dimension of the universe. Cepheids came into two different calculations of the scale of the universe. The incorrect calculation was done by Harlow Shapley, who misjudged the distance to the Magellanic cepheids and insisted that the Milky Way was the entire universe. The other one, using correctly-distanced cepheids to get intergalactic scale right on the money, was done by Edwin Hubble. You might have heard of him.


Although her remarkable discovery didn’t help her in her career, the relation of period and luminosity in variable stars earned Leavitt an enduring place in science history. Sadly, she died fairly soon after her discovery. If she had lived, many say she would have undoubtedly been given a Nobel Prize. And all that sprouting from a single astronomy course.

Image: NASA/CXC/JPL-Caltech/STScI



Via PBS, She Is An Astronomer, Carnegie Science.