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Henrietta Swan Leavitt
July 4, 2008, commemorated Henrietta Swan Leavitt's 140th birthday. Though Leavitt is not well-known for her contribution to astronomy, she was a very important character in the study of the universe. Born in 1868 in Lancaster, Massachusetts, Leavitt was the eldest child in a large Puritan family, and she was intelligent, excelling in the maths and sciences. In 1893, Edward C. Pickering introduced Leavitt to the Harvard College Observatory where she worked as a "computer," studying photographic plates of the stars and calculating stars' locations and luminosities. For hours, she sat at her desk next to the other computers looking at variable stars, or stars that wax and wan in brightness over a period of time.
In the midst of her observations, Leavitt noted a special kind of variable star, located in the Large and Small Magellanic Clouds. These stars, which are today known as Cepheids, were first discovered in 1784, but Leavitt devised a new law using these variable stars. In her 1912 paper announcing the discovery, she said that "A straight line can readily be drawn among each of the two series of points corresponding to maxima and minima, thus showing that there is a simple relation between the brightness of the variables and their periods." This became known as the Cepheid yardstick, meaning that distances in space could be measured according to the relative distances between stars. One could not, however, know the distance of a particular star from the earth.
Leavitt's law launched astronomers like Edwin Hubble into a quest to measure the universe. Using a mathematical process, called triangulation, astronomers used the sun as a baseline and began measuring. Leavitt would have continued her research in this area, but she was suffering from hearing loss and poor health and could no longer be as involved. She tried to keep working over the photographic plates when she passed away in 1921. In 1925, though Leavitt was nominated for a Nobel Prize and did not win, she did have a lunar crater named for her. While she seems undervalued for her work, Henrietta Leavitt was a wonderful woman and is still an important figure in astronomy.
* For more information, see:
Johnson, George. Miss Leavitt's Stars. NewYork: W.W. Norton & Co., 2005.
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