Henry Draper was a physician, but his passion was astronomy. At age 36, he left his positions as professor and dean of medicine at New York University to spend more time working in his observatory in Hastings-on-Hudson, New York.
On Henry Draper’s death in 1882, Harvard Observatory director Edward Pickering informed Anna Palmer Draper that he intended to carry out her husband’s desire to photograph and classify the stars, and she agreed to support and fund the work. As a result, the observatory’s largely-female staff became pioneers of astrophotography, spectral analysis, and astrophysics.
Dava Sobel’s book, The Glass Universe: How the Ladies of the Harvard Observatory Took the Measure of the Stars, describes how night after night and decade after decade, the women exposed glass plate negatives, capturing a spectrum for each star in the telescope’s field of vision by placing a prism in their telescopes. Annie Jump Cannon grouped the stars in their hundreds of thousands of photographs according to the character of each one’s spectrum and classified them into seven types designated by the letters O, B, A, F, G, K and M.
The 2014 television series Cosmos: A Spacetime Odyssey told of the Harvard women, as well, focusing on Cannon and Cecilia Payne in part of its eighth episode, Sisters of the Sun. Host Neil deGrasse Tyson emphasized not only Cannon’s classification system, but also—more than Sobol—the opposition initially provided for Payne’s important addition to it.
When Payne—an expert in theoretical and atomic physics—migrated from England to the United States in search of academic opportunity as a woman, she joined the Harvard team of researchers—now under director Harlow Shapley—and provided insight into the meaning of Cannon’s categories. Payne determined that, without knowing it, Cannon’s system had classified the stars from the hottest to the coldest.
By analyzing the chemical composition and physical state of the stars, Payne discovered that the stars are made almost entirely of hydrogen and helium; unlike on earth, all the other elements were present only in trace amounts. This contention was so stunning that it was initially disparaged by Princeton University professor Henry Norris Russell, the dean of American astronomers at the time, and Payne backed off the central claim of her thesis. But four years later, Russell affirmed that Payne was right.
Cosmos used this delayed acceptance to make a strong point about the uniqueness of the process of scientific discovery: “The words of the powerful may prevail in other spheres of human experience,” Tyson said. “But in science, the only thing that counts is the evidence and the logic of the argument itself.” Payne was quoted as saying, “I was to blame for not having pressed my point. I had given in to authority when I believed I was right. If you are sure of your facts, you should defend your position.”
The overriding impression of Sobol’s account of the work at Harvard Observatory is of passionate curiosity in the face of staggeringly tedious work which achieved a number of significant scientific discoveries:
- By Henrietta Leavitt:
- The brighter the magnitude of a star, the longer the period of its variation. Known as the period-luminosity relation, this became the fundamental method for determining the distance to a star.
- By Harlow Shapley:
- The universe is not centered on the sun, is magnitudes bigger than previously thought, and contains many other galaxies besides the Milky Way.
- By Cecilia Payne:
- The ratios of hydrogen and helium in the stars is a million times higher than on earth.
- The stars are similar to one another in chemical composition, but vary in temperature.