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https://newhumanist.org.uk/articles/6411/the-greatest-astronomy-phd-ever-written>
"Everyone knows that Isaac Newton discovered the law of gravity, and that
Charles Darwin discovered evolution by natural selection. But how many people
know that Cecilia Payne discovered what makes up the Universe?
This year marks a century since Payne, an English woman at Harvard university,
submitted the most important astrophysics PhD of the 20th century. Her
conclusion that the Sun – and by inference, the stars – is 98 per cent hydrogen
and helium, two elements virtually non-existent in their free form on Earth,
was initially dismissed by the most important astronomer in America. He later
took credit for her discovery, which was only attributed many years later.
Born in Buckinghamshire, Payne moved with her family to London to be near her
brother’s school – an early lesson that it was a man’s world. She nevertheless
obtained a place at Cambridge, where she studied physics. But, on completing
her studies, there was no opportunity for a woman to do a PhD. When a friend
told her that Harlow Shapley, director of the Harvard Observatory, was giving a
talk in London, she turned up and brazenly asked for a job.
Harvard was famous for its female “computers”, as they were called. Shapley
paid a pittance to dozens of these women, of varying education levels, to do
the labour-intensive work of classifying stars on thousands of glass
photographic plates. They included Annie Jump Cannon, who found that the
“spectra” of stars – how their light varied with colour – fit into a handful of
categories; and Henrietta Swan Leavitt, who discovered that “Cepheid variable”
stars could be used to measure the size of the Universe. But Payne declined a
job as a “computer”, as she wanted to do something more fundamental. That was
figuring out what the spectra of stars were actually telling us about their
make-up. (To give you an idea of how much her work was valued, her salary was
paid from a budget for “equipment expenses”.)
At the time, it was clear that each element in the Sun absorbed light at
characteristic colours, causing dips in the spectrum that were like an
elemental fingerprint. Each dip corresponded to the light absorbed when an
electron jumped from one atomic orbit to another. But there was a complication.
In the frenzy of the super-hot Sun, collisions between atoms stripped most of
them of their electrons. Fortunately, in 1920 the Indian physicist Meghnad Saha
wrote down an equation which, for any temperature, gave the fraction of each
element that had lost zero, one, two, and so on, electrons. Payne adapted this
equation to decode the solar spectrum. That was when she made her
groundbreaking discovery."
Via Susan ****
Cheers,
*** Xanni ***
--
mailto:xanni@xanadu.net Andrew Pam
http://xanadu.com.au/ Chief Scientist, Xanadu
https://glasswings.com.au/ Partner, Glass Wings
https://sericyb.com.au/ Manager, Serious Cybernetics
