![]() ![]() ![]() More than a century later, astronomers like Hartman are carrying on Leavitt's work. In doing so, they discovered that our universe is expanding, starting from a single point more than 14 billion years ago at the Big Bang-a discovery that would have never been possible without the discovery of the Leavitt Law. Using the period-luminosity relationship that Leavitt discovered, others later calculated the distances to Cepheid variables in galaxies outside our own Milky Way. Sadly, it was only after Leavitt's death from cancer at age 53 that astronomers realized that she had found the key to unlocking distances to such stars everywhere-whether in our Milky Way or in a galaxy in the distant universe. It took years for the mostly-male astronomy community to realize that this relationship (today known as "the Leavitt Law") means that measuring the period of a Cepheid variable immediately gives its true brightness-and furthermore, that comparing this to its apparent brightness immediately gives its distance. So in 1908 when Leavitt discovered a relationship between the brightness (or "luminosity") of a Cepheid variable star and the time it took to go through a full cycle of change (its "period"), her work was not immediately recognized for its significance. Although the work was demanding, it was not taken seriously by the male professional scientists of the time-it was seen as rote work not requiring intelligence or insight that could be done by anyone, even a woman. In the days before modern computers or even pocket calculators, a "computer" was a person hired to perform complex calculations in their mind, assisted only by pencil and paper. In fact, when Leavitt was first hired by Harvard College Observatory in 1895, she was hired as a "computer"-a term which meant something completely different from what it means today. Leavitt's contributions were largely ignored for one simple reason-she was a woman at time when women were not taken seriously as astronomers. The pattern was first noticed in 1784 in the constellation Cepheus in the northern sky, so these stars became known as "Cepheid variables." Cepheid variables went from interesting to completely indispensable in the early 1900s thanks to the work by astronomer Henrietta Leavitt. Hartman studied "Cepheid variables," a type of star that periodically pulses in and out, varying in brightness over the course of a few days or weeks. "It's been fascinating to work with such historically significant stars," says Kate Hartman, an undergraduate from Pomona College who announced the results at today's American Astronomical Society (AAS) meeting in National Harbor, Maryland.
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