Henrietta Swan Leavitt 1868-1921
One of the great pioneers of stellar physics Henrietta Swan Leavitt
died on December 12th, 1921.
She was born on July 4th, 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.
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.
Interestingly Delta Cephei the prototype Cepheid variable
star was discovered by John Goodricke in York in 1784. He was also deaf!
Leavitt died on December 12th, 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.
The asteroid 5383 Leavitt and the lunar crater Leavitt are
named in her honour.
