American astronomer, Henrietta Swan Leavitt is renowned for her discovery of the period-luminosity relation of Cepheid variables. This major discovery became the starting point for the ability of astronomers to determine the distance of stars from the earth. Her work transformed human understanding of the relative brightness and variability of stars.
On her discovery, Henrietta Swan Leavitt quoted:
“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.”
Early Life, Education and Career Achievements:
Born on July 4, 1868 in Lancaster, Massachusetts, Leavitt was the daughter of George Roswell Leavitt, a Congregationalist minister and his wife Henrietta Swan Kendrick. When she was a child, her family moved to Cleveland, Ohio.
Leavitt attended Oberlin College in 1885 and in 1892 graduated from the Society for the Collegiate Instruction for Women (now known as Radcliffe College). After her graduation, Leavitt remained in school an additional year to take further astronomy courses. 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 under the astronomer Edward Pickering, who had initiated a research program on the measurement of stellar magnitudes. Seven years later, in 1902, Pickering hired Leavitt to the Observatory’s permanent staff at $.30 per hour, and she worked there until her death.
As an assistant at Harvard College Observatory, though she was talented enough, 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 assigned the tedious task of cataloguing “variable” stars, whose brightness appears to ebb and flow in predictable patterns.
While investigating the Magellanic Clouds (neighbor-galaxies of the Milky Way), Leavitt revealed 1,777 new variable stars. More importantly, in 1912, by comparing different photographs of the same variable star, Leavitt established that stars of the “Cepheid” type had bright-dim cycle periods inversely proportionate to their magnitude (the stronger the star, the slower its cycle).
Leavitt found out that the variable stars’ cycles must depend not on how dazzling they appear (“apparent” luminosity), but how bright they really are (“intrinsic” or “absolute” luminosity). Later, Leavitt devised a period-luminosity ratio that applies to all Cepheid stars and which enabled astronomers to calculate the distance from Earth to any visible Cepheid star in the universe.
Pickering did not allow Leavitt to follow up on her ground-breaking discovery, and continued to treat her as a mere lab assistant. Her efforts would have won her a Nobel Prize but she died of cancer in 1921 at age fifty-three. The asteroid 5383 Leavitt and the crater Leavitt on the Moon are named after her to honor deaf men and women who have worked as astronomers.