Henrietta Swan Leavitt was born in Lancaster, Massachusetts,
and graduated from Radcliffe College in 1892. In 1902 she became a permanent staff
member of the Harvard College Observatory (HCO) and through her scientific ability quickly rose
to head the department of photographic stellar photometry.
During her tenure at Harvard, she spent a great deal of
time searching photographic plates of the night sky searching for variable stars in both the
Large Magellanic Clouds (LMC) and Small Magellanic Clouds
(SMC). In 1904, using a rather laborious process called
superposition, she discovered 152 variable stars in
the LMC and 59 in the SMC. Over the next year she
reported 843 new variables in the SMC. These discoveries led Charles Young of Princeton to
remark in a letter to HCO director E. C. Pickering, "What a variable-star 'fiend' Miss Leavitt is,
one can't keep up with the roll of the new discoveries."
Probably Leavitt's greatest discovery came from her study
of 1,777 variable stars in the Magellanic Clouds. She was able to determine the periods
of 25 Cepheid variables in the SMC and in 1912 she announced
what has since become known as the famous Period-Luminosity relation --
"A straight line can be readily 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
variable and their periods."
At the same time, Leavitt also realized that --
"Since the variables are probably the same distance from the Earth, their periods may be
associated with their actual emission of light, as determined by their mass, density, and
surface brightness."
Today the Period-Luminosity relation is one of the backbones of
the "distance ladder" and is used to calculate the distances to other galaxies.
In the course of her work, Leavitt also discovered four
novae and some 2,400 variable stars (about half of the total
known at the time). She also extensively studied Algol-type eclipsing
binary stars as well as asteroids. She was an active member
in many clubs and societies, which included Phi Beta Kappa, the American Astronomical and
Astrophysical Society, The American Association for the Advancement of Science, The American
Association of University Women, and she was an honorary member of the American Association of
Variable Star Observers.
Henrietta Leavitt died of cancer in 1921 before her work
on the new photographic magnitude scale was completed. Her death was viewed as a "near
casastrophe" by many of her colleagues. Hovever, her important contribution to scientific
advancement was internationally acknowledged and in 1925, the Swedish Academy of Sciences
nominated her for the highly coveted Nobel Prize.
