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Leavitt's study of stars' brightness helped pinpoint astral distances
Thursday, March 09, 2000
Early in the 20th century, many of the best astronomers in the world could be found at the Harvard University observatory. There, Henrietta Swan Leavitt and other women analyzed data and made astronomical calculations.
Leavitt was born in Cambridge, Mass., and graduated in 1892 from the school that became Radcliffe College.
Leavitt became interested in astronomy as a college senior. Shortly after graduation, she suffered from a severe illness that kept her confined to home and ultimately left her nearly deaf. In 1895, she began to volunteer at the observatory, and by 1902, she had earned a staff position in the computing department.
Leavitt was assigned to stars that change in brightness, called variables. Using photographic plates, Leavitt discovered some 2,500 variable stars. She developed a technique for measuring star brightness from photographs that became the accepted practice worldwide and became known as the "Harvard Standard." More importantly, she recognized a pattern in the stars.
Leavitt noticed that a particular type of variable stars -- called Cepheid variables -- had an interesting characteristic. She demonstrated the time it took for the stars to change in brightness was directly related to their brightness. Using this information, astronomers could calculate the distance to these stars. By looking for Cepheid variables in other galaxies, Edwin Hubble was able to calculate distances to those galaxies and determine the rate of expansion of the universe.
-- By John G. Radzilowicz, director, Henry Buhl, Jr. Planetarium & Observatory
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