Pointing the way

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.