Henrietta Swan Leavitt


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Henrietta Swan Leavitt was an astronomer who worked at the Harvard College Observatory at the turn of the twentieth century.

Leavitt was born in in Lancaster, Massachusetts, in 1868 and grew up in Cleveland, Ohio. She attended Oberlin College and later went to Radcliffe College, then called the Society for the Collegiate Instruction for Women, and graduated with a bachelor’s degree in 1892.

In 1893, she was hired by Edward Charles Pickering, an astronomer and physicist, to work under him at the Harvard College Observatory. Pickering hired about a dozen skilled women to work under him to process astronomical data and analyze stellar spectra. This staff came to be called the ‘Harvard Computers,’ or more mockingly by the male-dominated scientific community as ‘Pickering’s Harem.' In the late nineteenth and early twentieth century, many leading male scientists hired a bevy of subordinate females, who were seen as less threatening and were also cheaper. This is known as the ‘Harem effect’ in the history of science. Initially Leavitt worked as a volunteer as she had an independent sources of income. Later she was paid 30 cents an hour, or around $10.50 a week.

From the start of her work, Leavitt developed a standard of photographic measurement, the ‘Harvard Standard,’ that the International Committee of Photographic Magnitudes accepted in 1912. Leavitt was also assigned the task of studying and cataloging variable stars, whose luminosity varied with time. Leavitt discovered more than 2,400 variable stars and also found that they changed their brightness and dimness in a fairly regular pattern. There was a direct correlation between the time taken and the star’s luminosity. This led her to establish the Cepheid variable period-luminosity relationship, an unexpected insight that opened the universe to measurement and, eventually, confirmation of its expansion.  In 1908 she published her results in the Annals of the Astronomical Observatory of Harvard CollegeLeavitt could only work sporadically at Harvard, however, as she suffered from an illness which made her increasingly deaf.  In 1921, before she died of cancer on 12 December, Leavitt became the head of the stellar photographic photometry department at Harvard, which studied photographs of stars to determine their magnitude. 

Leavitt received little recognition during her lifetime. She could not pursue her own topics of research and worked on whatever Pickering assigned to her. Her discoveries, especially the period-luminosity relationship, later paved the way for the discoveries of other astronomers, particularly Edwin Hubble. In 1925, Magnus Gustaf (Gösta) Mittag-Leffler of the Swedish Academy of Sciences proposed to nominate her for the Nobel Prize in Physics, not knowing that she had died four years before.

Leavitt was a member of the American Association of University Women, the American Astronomical and Astrophysical Society, the American Association for the Advancement of Science and an honorary member of the American Association of Variable Star Observers. The asteroid 5383 Leavitt and the lunar crater Leavitt were named in her honor.

Further Reading

George Johnson, Miss Leavitt's Stars: The Untold Story of the Woman who Discovered how to Measure the Universe (New York: W. W. Norton, 2005).

Henrietta S. Leavitt, "1777 Variables in the Magellanic Clouds," Annals of Harvard College Observatory LX, No. iv (1908), p. 87-108.

[Henrietta S. Leavitt and] Edward C. Pickering, "Periods of 25 Variable Stars in the Small Magellanic Cloud," Harvard College Observatory Circular 173 (March 1912), p.1-3.

Matthew S. Luckett, “'The Widening of the Horizon:'” Gender, the Body, and 'Women’s Work' at the Harvard Observatory, 1880-1925," History 297 seminar paper for Prof. Mary Terrall, UCLA. c. 2006.

Pamela E. Mack, "Strategies and Compromises - Women in Astronomy at Harvard College Observatory 1870-1920," Journal for the History of Astronomy 21, No. 1 (February 1990), p. 65-76.

Pangratios Papacosta, "Nobel Prize for a 'Computer' named Henrietta Leavitt (1868–1921)," paper based on poster presented at AAS annual meeting, Denver, 2004.

‘Harvard Computers,’

‘Pickering’s Harem.’