Henrietta Swan Leavitt

Last night I ended up watching a documentary about space. Space has always fascinated me, not just because of its vastness, but mostly because of the mystery that still surrounds it despite the incredible discoveries made by modern day scientists. With all our knowledge, technology and supercomputers we practically still know only a fraction of what there’s to know about space. That puts our daily life into a new perspective, doesn’t it?

Anyway, back to the documentary. Any docu about space-time, the stars and planets, can’t go without mentioning Einstein and Hubble. There was also talk about Euclid and euclidean geometry, and later about noneuclidean geometry which was discovered by Gauss and Bernhard Riemann. William Herschel, a German-born astronomer who moved to Bath, manufactured a new type of telescopes which allowed the astronomers to see the sky better. He did it with the help of his sister, a fellow astronomer, Caroline Herschel. While I’ve heard of William Herschel, I’ve never heard of her and her contribution to our knowledge of space before.

leavitt_aavsoBut there was another figure with an even greater contribution to the science who is rarely mentioned despite the vital  importance of her discovery. Henrietta Leavitt worked in the Harvard College Observatory (at first for free, later she was paid 10 dollars per week!) where she catalogued the brightness of stars from photographic plates.

Until then, the distance between stars was measured with the help of stellar parallax. But with the help of the parallax, astronomers could only measure I small percentage of our galaxy. They needed a new method to measure the stars further away.

Cepheids are a class of star which change their brightness over time in a repeating pattern. It was Leavitt who discovered, in 1902, that the repeating pattern changes depending on how intrinsically bright the star is. So the speed of the Cepheid’s pulse can be used to tell if it’s faint in our skies because it’s naturally dim or because it’s far away. The period–luminosity relationship for Cepheids is now known as “Leavitt’s law“, and it allowed scientists to compute the distance to galaxies which were too remote for stellar parallax observations to work. But Leavitt herself couldn’t further her discoveries because, as a woman, she was not allowed to operate a telescope! Furthermore, she was often ill and she was slowly losing her hearing. She died of cancer, aged 53.

Her work became the basis for the work and discoveries of many future astronomers, including Edwin Hubble.


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