Science has traditionally been a men matter. Nevertheless, this unfair rule was broken by
three courageous women who decided study stars and achieved unprecedented
results in this field. Her names were Henrietta Swan Leavitt (1868-1921),
Cecilia Payne – Gaposchkin (1900 - 1979) and Jocelin Bell (1943-).
Henrietta Swan Leavitt was born in
Massachusetts (US) in an important date for her country, the July 4 of 1868.
She graduate in a women institution, the Society for the Collegiate Instruction
of Women in 1892. Following an interest aroused in her senior year, she became
a volunteer assistant in the Harvard Observatory in 1895. Some years after, she
was admitted in a women - composed research group directed by Edward C.
Pickering with the mission to determine the brightnesses of all measurable
stars by photometry. The reason to choose women for this project was double,
the work was considered tedious and repetitive, without necessity to have a
high degree of intelligence, and the salary was considerably less than men.
Henrietta was especially good in her work, and soon advanced from routine work
to a position as head of the photographic stellar photometry department.
Leavitt’s outstanding achievement was her discovery in 1912 that in a certain
class of variable stars, the Cepheid variables, the period of the cycle of
fluctuation in brightness is highly regular and is determined by the actual
luminosity of the star. If you know the period of a Cepheid you can calculate
its actual luminosity, and measuring its luminosity you can calculate the
distance to that Cepheid. This discovery leaded to a new method to accurately
determine the distances of many Cepheid stars and consequently of the star
clusters and galaxies in which they were observed. The most dramatic
application was Hubble’s use in 1924 of a Cepheid variable to determine the
distance to the great nebula in Andromeda, which was the first distance
measurement for a galaxy outside the Milky Way. This measurement changed our
concept of the Universe, because we learned that there are millions and
millions of different galaxies in the Universe and not only one, our galaxy.
Cecilia Payne – Gaposchkin was born in
Wendoven, England, in 1900. She entered the University of Cambridge in 1919. A
lecture by astronomer Sir Arthur Eddington on his expedition to the island of
Principe that confirmed Einstein’s theory of general relativity inspired her to
become an astronomer. Eddington encouraged her ambition, but she felt there
were more opportunities for a woman to work in astronomy in the US than in
Britain. In 1923 she received a fellowship to study at the Harvard College
Observatory in Cambridge. In her Ph.D. thesis (published as Stellar Atmospheres
1925), Payne used the spectral lines of many different elements to establish
that the spectral sequence did correspond to quantifiable stellar temperatures,
and also determined that stars are composed mostly of hydrogen and helium.
However, she was dissuaded from this conclusion by astronomer Henry Norris
Russell who thought that stars would have the same composition as Earth, but
finally, Russell conceded in 1929 that Payne was correct. Payne received the
first Ph.D. in astronomy from Radcliffe College for her thesis, since Harvard
did not grant doctoral degrees to women. Some astronomers thought that her
thesis was the most brilliant Ph.D. thesis ever written in astronomy.
Jocelin Bell Burnell was born in Northern
Ireland in 1943. She studied astrophysics and as a postgraduate student discovered
in 1967 a peculiar radio signal from space that tracked across the sky with the
stars. She established that the signal was pulsing with great regularity, at a
rate of about one pulse every one and third seconds. Temporarily dubbed “Little
Green Man 1” the source was identified after several years as a rapidly rating
neutron star. That was the first discovered “pulsar”, one of the most
interesting objects in the universe, sometimes a previous stage to a black hole.
His thesis director was awarded by the Nobel prize for this discovery, but she
was never recognized for it.
In my opinion is necessary to recognize these
three women because they pointed the way to other scientist women and
contributed to our world with knowledge but with justice too.
