Henrietta Swan Leavitt (1868-1921) made a discovery that forever changed the field of astronomy. Born in Lancaster, Massachusetts on July 4th, 1868, to Congregational minister Dr. George Roswell Leavitt and his wife, Henrietta Swan Kendrick, Leavitt was the oldest of seven children. She attended Oberlin College, the earliest coeducational college in the United States, and later enrolled in the Society for the Collegiate Instruction for Women—later known as Radcliffe College—where  many Harvard professors had informal teaching arrangements with women studying astronomy at the Harvard College Observatory. Graduating in 1892, Leavitt received a certificate which would have been equivalent to a Harvard College Bachelor of Arts Degree, had she been a man.

In 1895, with the financial support of her parents, Leavitt volunteered at the Harvard College Observatory where Director Edward C. Pickering engaged her to study the observatory telescope’s photographic plates to tabulate the color, position and magnitude of the stars with particular attention on variable stars.

Pickering eventually offered Leavitt a paid position as a “computer” at thirty cents an hour.

During this time computers were not machines, but primarily women who did the tedious, repetitive calculations and record keeping necessary to track the observatory’s findings. Working in a dingy room beside other well-educated women, she analyzed and documented the growing volume of telescope images and related notations made by men who worked at night with the telescopes. These women, known as “Pickering’s harem,” were rarely credited for their diligent research and intelligence.

Leavitt identified 1,777 variable stars—those that change from bright to dim and back over fairly regular periods—in the Small and Large Magellan Clouds. Working with a magnifying glass, she painstakingly examined the positive and negative photographic plates and observed a direct relationship between the time it took a star to go from bright  to dim and its absolute brightness, or magnitude and distance, from Earth. Her discovery of the Cepheid Variable Period-Luminosity relationship, known today as Leavitt’s Law, documented the ability to accurately calculate distances from the Earth and was published in a 1912 paper, under the name of Director Pickering.

Leavitt ultimately identified over 2,400 variable stars. She developed the internationally accepted Harvard Standard, a standard of photographic measurement that ordered stars over seventeen magnitudes of brightness. She was named Head of Stellar Photometry at the Harvard College Observatory in 1921, but did not live long enough to enjoy her new role. She died on December 12, 1921 at the age of 53.

Her death was largely unnoticed by the scientific community. Four years later, the head of the Swedish Academy of Sciences sent a letter to her, writing, “your admirable discovery … has impressed me so deeply that I feel seriously inclined to nominate you to the Nobel Prize in Physics for 1926.” As Nobel Prizes are not awarded posthumously, her work could not receive this prestigious recognition.

Leavitt’s groundbreaking discovery—now over 100 years ago—paved the way for discoveries by many other astronomers, including Edwin Hubble, and shines brightly in a universe of women who changed our world.