Cecilia Payne-Gaposchkin

Cecilia Payne-Gaposchkin (born Cecilia Helena Payne; May 10, 1900 – December 7, 1979) was a British-born American astronomer and astrophysicist who proposed in her 1925 doctoral thesis that stars were composed primarily of hydrogen and helium.

Her groundbreaking conclusion was initially rejected because it contradicted the scientific wisdom of the time, which held that there were no significant elemental differences between the Sun and Earth.

Independent observations eventually proved she was correct.

Her work on the nature of variable stars was foundational to modern astrophysics.

Cecilia Helena Payne was one of three children born in Wendover in Buckinghamshire, England, to Emma Leonora Helena (née Pertz) and Edward John Payne, a London barrister, historian and musician who had been an Oxford fellow.

Her mother came from a Prussian family and had two distinguished uncles, historian Georg Heinrich Pertz and the Swedenborgian writer James John Garth Wilkinson; her sister Florence was a pianist.

Cecilia Payne's father died when she was four years old, forcing her mother to raise the family on her own.

Cecilia Payne began school in Wendover at a private school run by Elizabeth Edwards.

When she was twelve her mother moved to London for the sake of the education of Cecilia's brother Humfry, who later became an archaeologist.

In 1914, he had written in an academic article:

The agreement of the solar and terrestrial lists is such as to confirm very strongly Rowland's opinion that, if the Earth's crust should be raised to the temperature of the Sun's atmosphere, it would give a very similar absorption spectrum.

The spectra of the Sun and other stars were similar, so it appeared that the relative abundance of elements in the universe was like that in Earth's crust.

Payne consequently described her results as "spurious".

A few years later, astronomer Otto Struve described her work as "the most brilliant PhD thesis ever written in astronomy".

Russell also realized she was correct when he derived the same results by different means.

Cecilia attended St Mary's College, Paddington, where she was unable to study much mathematics or science, but in 1918 changed schools for St Paul's Girls' School.

There she was urged by Gustav Holst, who taught music at the school, to pursue a career in music, but she preferred to focus on science.

The following year she won a scholarship that paid all her expenses at Newnham College, Cambridge University, where she initially read botany, physics, and chemistry but she dropped botany after her first year.

Her interest in astronomy began after she attended a lecture by Arthur Eddington on his 1919 expedition to the island of Príncipe in the Gulf of Guinea off the west coast of Africa to observe and photograph the stars near a solar eclipse as a test of Albert Einstein's general theory of relativity.

She said of the lecture: "The result was a complete transformation of my world picture. [...] My world had been so shaken that I experienced something very like a nervous breakdown."

Adelaide Ames had become the first student on the fellowship in 1922; the second was Payne.

She was described by Lawrence H. Aller as one of the "most capable go-getters" in Shapley's group.

After being introduced to Harlow Shapley, the Director of the Harvard College Observatory, where he had just established a graduate program in astronomy, she left England in 1923.

This was made possible by a fellowship to encourage women to study at the observatory.

Shapley persuaded Payne to write a doctoral dissertation, and so in 1925 she became the first person to earn a PhD in astronomy from Radcliffe College of Harvard University.

Her thesis title was Stellar Atmospheres; A Contribution to the Observational Study of High Temperature in the Reversing Layers of Stars.

Payne was able to accurately relate the spectral classes of stars to their actual temperatures by applying Indian physicist Meghnad Saha's ionization theory.

She showed that the great variation in stellar absorption lines was due to differing amounts of ionization at different temperatures, not to different amounts of elements.

She found that silicon, carbon, and other common metals seen in the Sun's spectrum were present in about the same relative amounts as on Earth, in agreement with the accepted belief of the time, which held that the stars had approximately the same elemental composition as the Earth.

However, she found that helium and particularly hydrogen were vastly more abundant (for hydrogen, by a factor of about one million).

Her thesis concluded that hydrogen was the overwhelming constituent of stars, making it the most abundant element in the Universe.

However, when Payne's dissertation was reviewed, astronomer Henry Norris Russell, who stood by the theories of American physicist Henry Rowland, dissuaded her from concluding that the composition of the Sun was predominantly hydrogen because it would contradict the scientific consensus of the time that the elemental composition of the Sun and the Earth were similar.

Accepted ratios for hydrogen and helium in the Milky Way Galaxy are ~74% hydrogen and ~24% helium, confirming the results of Payne-Gaposchkin's calculations from 1925.

After her doctorate, Payne studied stars of high luminosity to understand the structure of the Milky Way.

Later she surveyed all stars brighter than the tenth magnitude.

She then studied variable stars, making over 1,250,000 observations with her assistants.

In 1929, he published his findings in a paper that briefly acknowledged Payne's earlier work and discovery, including the mention that "[t]he most important previous determination of the abundance of the elements by astrophysical means is that by Miss Payne [...]".

Nevertheless, he was generally credited for the conclusions she reached.

She completed her studies, but was not awarded a degree because of her sex; Cambridge did not grant degrees to women until 1948.

Payne realized that her only career option in the U.K. was to become a teacher, so she looked for grants that would enable her to move to the United States.