“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.”
Henrietta Swan Leavitt - Lady of Luminosity
Henrietta Swan Leavitt was born on July 4, 1868 in Lancaster, Massachusetts. As a young child, her family moved to Cleveland, Ohio. Leavitt attended Oberlin College and in 1892 graduated from the Society for the Collegiate Instruction for Women, now known as Radcliffe College. She then traveled in America and in Europe during which time she lost her hearing. Three years after graduation, she became a volunteer research assistant at Harvard College Observatory. Seven years later, in 1902, Pickering hired her on the permanent staff at $.30 per hour.
Leavitt’s interest in astronomy began during her senior year in college when she took an astronomy class. She furthered her studies in astronomy with graduate work. As an assistant at Harvard College Observatory, though she had the ability, she was given little theoretical work. Pickering did not like his female staff to pursue such endeavors. Instead, she was given the position of chief of the photographic photometry department and was responsible for the care of telescopes.
Leavitt also was required to perform research from the observatory’s photographic plates collection. Using the plates, she was to determine a star’s magnitude. There was no standard for ascertaining magnitudes at the time. Leavitt devised a system, using “the north polar sequence” as a gage of brightness for stars during her investigations. This was quickly recognized by the scientific community as an important standard and in 1913, was adopted by the International Committee on Photographic Magnitudes.
Another area of research that Leavitt pursued was on variable stars and in 1908 she made her most important discovery. By studying Cepheid variables in the Small Magellanic Cloud, which are all about the same distance from Earth, Leavitt determined the absolute magnitudes of stars. Her study led to the period-luminosity relationship of these variables, which in turn led to the ability to determine distances of stars from a mere one hundred light years to ten million light years. Ejnar Hertzsprung used her discovery to plot the distance of stars; Harlow Shapley used it to measure the size of the Milky Way; and Edwin Hubble used her work to ascertain the age of the Universe.
Leavitt died on December 21, 1921 from cancer. During her lifetime, she discovered over 1,200 variable stars, half the number of all such objects known at the time of her death. She was also a member of many organizations and a proponent for women in astronomy. She made monumental contributions to the advancement of astronomy and our understanding of our place in the Universe. There is no way of knowing what other contributions she would have made had she not died so young.
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