Breakthrough: The Ideas That Changed the World

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Narrator

We'd successfully brought the stars closer, but how close were they? Astronomy needed a yardstick to give scale to our vision. And unexpectedly, it would come from a boom in real estate. In the 1840s, New York was on the up. Investors were lining up to pour money into a building boom in the Big Apple. Entrepreneur Courtlandt Palmer was about to make a fortune in Manhattan. By the time he died in 1874, he was a multimillionaire and left his money to his children. His daughter, Mary Anna Palmer Draper, was married to a pioneer of astrophotography. Convinced of its potential, she made a substantial donation to Harvard University for a major astronomy project. The Harvard Observatory at the time was very interested in astrophotography and wanted to make an entire map of the sky with these photographs that were taken both in the northern and the southern hemisphere. (lively music) So now that you have thousands of photographs, you needed a team to organize them and study them. The Harvard observatory hired a team of women who were specifically studying the stars using glass plates, which was very unusual back then, because there weren't very many women working in the sciences. So these women did number crunching all day and that's why they were known as the human computers. (energetic music) Some of the women that were working here, their job was to measure the brightness of stars. Some of the tools that these women used included fly spankers, which were tiny little pieces of glass plates that had different sized stars on them. It was called a fly spanker because it was too little to do a fly much damage. So as you can see, there are different sized dots with numbers written next to them, and these were used as the standard for measuring. So say you wanted to measure this little A star here. You could bring up your fly spanker and try to find the best match, and then that was the brightness of your star. -

Narrator

But this impressive star catalog

was missing vital information

distance. After all, if two stars have identical brightness as seen from the Earth, it doesn't mean they are the same distance away. One star could be quite dim in reality, yet quite close, and the other huge and powerful but a long way off, and still they would look the same from Earth. Without knowing the true brightness of a star, astronomers had no idea how far away it was. But one woman had an idea. Henrietta Leavitt was known for being a very meticulous worker. She often stayed late into the evening to make sure she measured all the stars that she wanted to measure that day, and I think that really comes through when you look at her notes. Through this very meticulous approach, she was able to have a breakthrough that is now known as the Leavitt Law. -

Narrator

was missing vital information

Leavitt's law is a little complex, but it's the key to unlocking the universe. There are some stars that regularly get slightly dimmer over time, before returning to their former glory. These variable stars have a kind of heartbeat or brightness. Leavitt studied a group of them and discovered that the dimmer ones beat quickly. The ones that are brighter beat more slowly. It's as if the big, bright stars have a slow heartbeat and the smaller, dimmer ones a fast one. Find a variable star anywhere in the sky, and its heartbeat gives its true brightness away. Now its distance can be measured by how bright it appears from the Earth. And bam, you have a yardstick for astronomers so that they could start to measure distances in space in ways that they couldn't do before. For the first time, astronomers were able to understand exactly how large our galaxy is. So this 19th-century property boom in New York had accidentally unlocked the scale of the universe.