That the sun generates light and heat is obvious; how it does it is not.
Working out how the Sun works is the result of many remarkably able and talented investigators.
In 1925, Cecilia Payne's Ph.D. thesis "changed the Universe" by revealing what lay at the Sun's heart.
Even before Cecelia was born in 1900, it was obvious that the heat from the Sun was generated differently from what we experience on Earth. The wood or other fuel in a chemical fire burns down to nothing but ash, while the Sun's fire appears not to consume it. If its energy cannot be attributed to chemical burning, then how could it be accounted for?
Perhaps the Sun's energy was related to the radioactive elements discovered in the late 19th century. After all, uranium seemed able to pump out energy without diminishing to ash.
Using spectrometers, a technology invented early in the century and demonstrated to be effective at identifying elements around 1859, scientists began to collect and interpret solar spectra, searching for the uranium, radium, or thorium.
Instead, the pattern of colors and dark absorption lines that appeared in spectrometers sent the message that the composition of the Sun mirrored the composition of Earth. The large amounts of iron on Earth, seemed to mirror the large amounts of iron on the Sun. These data ended speculation about a radioactive source of the Sun's energy.
The laws of thermodynamics heat were invoked by Lord Kelvin, the dean of 19th century physics, and his German colleague von Helmholtz to explain the Sun's heat. Its source was the "gravitational energy released in the original collapse of matter," making the Sun "a giant ball of very hot, incandescent fluid." Since the Sun was still hot it could be inferred that the Sun must be quite new, perhaps only 10,000,000-20,000,000 years old. (Kahana, 2015)
This is where things stood when Cecilia won a scholarship to Newnham College, the women's college at Cambridge University.
Sir Ernest Rutherford, the discoverer of the atomic nucleus, was teaching and mentoring the famous young men who would shape modern atomic physics, Nels Bohr, James Chadwick, and many others.
But for Clarice, being taught by Rutherford was less than inspiring. This was because however "great Rutherford was with his male students, he was not prepared to do the same for his women students. While with male students Rutherford "was bluff and friendly, but with women he was bluff and pretty much a thug. He was cruel to [Payne] at lectures, trying to get all the male students to laugh at this one female in their midst. It didn't stop her from going--she could hold her own with his best students in tutorials--but even forty years later, retired from her professorship at Harvard, she remembered the rows of braying young men, nervously trying to do what their teacher expected of them." (Bodanis, 2000, p.175)
In contrast, another notable Cambridge professor Sir Arthur Eddington was happy to work with the obviously brilliant young woman. From Eddington, "Payne picked up Eddington's barely stated awe at the potential power of pure thought. He liked to show how creatures who lived on a planet entirely shrouded in cloud would be able to deduce the main features of the unseen universe above them." (Bodanis, p. 176)
Eddington also got her working on the problem of what fueled the Sun and the stars.
But in 1919 Cecilia realized she wouldn't be able to conduct research in Great Britain when the most powerful professor in the country was disparaging of women's talents.
She applied to and was accepted into Harvard's Ph.D. program in astronomy to work with Harlow Shapley, one of the the United States' most well-known astronomers.
She chose to work on the problem of stellar interiors as her dissertation topic. Later, Payne was to reflect that once she began her work, "There followed months, almost a year...of bewilderment. Often I was in a state of exhaustion and despair, working all day and late into the night" because what she was finding in the examination of the spectrometric data contradicted the accepted explanations.
As Henry Norris Russell and Henry Rowland, two of the most important American physicists put it, "if the Earth's crust should be raised to the temperature of the Sun's atmosphere, it would give a very similar absorption spectrum." (Williams, 2015)
An ordinary graduate student who knew what he was supposed to find; that is, iron, would have read the spectrometric data in the orthodox way. But Payne wasn't ordinary and her study of spectrometric data led her to understand that this data, like all data, did not "speak for itself" but required interpretation, and insuring that her interpretation wasn't driven by bias but by the data.
Payne began at the beginning: making sure that she was reading the data correctly. As Richard Feynman put it much later, " The first job of the scientist is to be sure you are not fooling yourself; and you are the easiest one to fool."
Using the most recent research about the behavior of elements in extreme heat, led Payne to conclude that the dominant elements on the Sun were hydrogen and helium rather than iron. (Williams, 2014)
Even before her thesis was completed in January of 1925, word of her radical findings leaked out and caused an academic ruckus. The professors who had built their reputations on the iron content on the Sun were appalled that this young woman was saying that the Sun was composed of hydrogen and helium.
Letters were exchanged between Payne and Russell, that if she wanted to get her research accepted she'd have to recant. In her own published thesis she had to insert the humiliating line: "The enormous abundance [of hydrogen]...is almost certainly not real." (Bodanis, p. 181)
It took several years but independent research confirmed Payne's data.
The importance of her work was that it made possible the application of "E=mc^2 to explain the fires of the sun. She had shown that the right fuel was floating up in space; that the sun and all the stars we see actually are great E=mc^2 pumping stations." (Bodanis, 2000, p. 181)
Her career at Harvard prospered. She became the first woman professor and the first woman who was a department chair.
Bodanis, David (2000). E=mc2 : The Biography of the World's most Famous Equation. Walker & Company: New York.
Kahana, David (2014). Before Einstein how did people think the Sun worked? Quora. Retrieved from https://www.quora.com/Before-Einstein-how-did-people-think-the-Sun-worked
Williams, Richard (2015). January 1, 1925, Cecilia Payne-Gaposchkin and the Day the Universe Changed. The American Physical Society. APA News The Month in Physics History, January 2015. Vol. 24 Number 1. Retrieved from https://www.aps.org/publications/apsnews/201501/physicshistory.cfm
Dr. John Holton
Dr. John Holton joined the S²TEM Centers SC in July of 2013, as a research associate with an emphasis on the STEM literature including state and local STEM plans from around the nation.