Henrietta Swan Leavitt
July 4, 1868 – December 12, 1921
Henrietta Swan Leavitt
Born on the 4th of July, Henrietta was an American astronomer who discovered the relation between the luminosity and the period of Cepheid variable stars, which allowed us to measure the distance to faraway galaxies.
According to Wikipedia: Leavitt was a graduate of Radcliffe College. In 1893, Leavitt began working at the Harvard College Observatory as one of the women human “computers” hired by Edward Charles Pickering to measure and catalog the brightness of stars as they appeared in the observatory’s photographic plate collection. (In the early 1900s, women were not allowed to operate telescopes)
Because Leavitt had independent means, Pickering initially did not have to pay her. Later, she received $0.30 an hour for her work. Though she received little recognition in her lifetime, it was her discovery that first allowed astronomers to measure the distance between the Earth and faraway galaxies.
She explained her discovery:
“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.”
This means each galaxy emits a light that has a periodic pulse. If we have two galaxies and one of them is twice as far away as the second on, the galaxy that is further away looks very dim in comparison, however, if the light is pulsing at the same rate we can tell that the brightness of both galaxies are equivalent.
After Leavitt’s death, Edwin Hubble used the luminosity-period relation for Cepheids together with spectral shifts first measured by fellow astronomer Vesto Slipher at Lowell Observatory to determine that the universe is expanding (see Hubble’s law).
