The Ladies of Observatory Hill (
· Before 1859 there were no working female astronomers
(Caroline Lucretia Herschel was the Astronomer-sister of Sir William Herschel, discoverer of Uranus. Annie Russell Maunder’s contributions were presented as those of her husband Edward Walter Maunder, discoverer of the Maunder minimum in sunspot activity.)
· Between 1859 and 1940 one-of-three astronomers was a woman.
What happened? Photography was invented and great piles of data requiring time-consuming analysis became available.
· Yet – no women’s names appear in textbooks of astronomy for this period. They were hired to do simple tasks, but were not allowed to marry or to progress professionally. Their average time of employment was 5 years.
Annie Jump Cannon (Born 1863 in Dover Delaware, Died 1941)
· Photographed millions of stars with a prism-equipped telescope.
· Catalogued them by “star type.” Could recognize spectral lines where others saw only a smudge. Her measurements were later confirmed by others with modern equipment.
· Not interested in “The Grand Fact.” She never asked “why” and considered such questions to be an impediment to her task.
· Since there was no male to attribute her work to, it is now known as the “Harvard System” (but not the “Cannon” system.)
Inspired as a young girl by a lecture of Arthur Eddington. Studied at
· She examined the spectral lines, not only in terms of the Boltzmann equation, but also the Saha equation.
Boltzmann – distribution of excited states as function of T;
Saha – distribution of charge states (ionization) as function of T
· Only the visible spectrum was then accessible. She found lots of hydrogen, but H is not a good tool for ground state absorption in in the UV, which doesn’t get through the atmosphere.
· She tried H and K lines of Ca II (isoelectronic to K I). Here the 4s-4p transition at around 4000 A does get through.
· She discovered that all stellar objects have essentially the same elements in the same abundances, with hydrogen 60-80% and H + He 96-99%. She published it in her thesis in 1925.
· Henry Norris Russell and Arthur Eddington had their own model that identified iron as the most abundant element, in disagreement with Payne’s findings of an overwhelming abundance of hydrogen. They mounted an aggressive offense against her, and she was powerless to defend against them. Unlike Galileo, she was not threatened with torture and imprisonment. However, she was forced to recant and to remain silent about her discovery concerning hydrogen in order to retain her position.
· In 1929 new evidence became available which caused Russell to flip, and he wrote a book and took credit for the discovery.