Tuesday I wrote about a book by Dava Sobel from 2016. 

The Glass Universe: How the Ladies of the Harvard Observatory Took the Measure of the Stars. Dava Sobel. Viking. 2016. 

I’ve been rereading it. Sobel is a remarkable writer, able to explain scientific concepts clearly. This can deceive the reader into thinking a topic has been understood — until the reader tries to explain it to someone else. I saw this ALL the time when I was teaching. The first step towards knowledge is to hear what is actually being said, and understand it, as long as someone else is talking. That’s just not the Last step. 

Sobel explains the importance of variable stars, the importance of the women Harvard Observatory hired to catalogue this variability, and the importance of the record of the variability in photographs taken with the telescopes used by Harvard and others. She also explains how the photographs proved various things, and I had to go back and work hard to understand the actual science she was discussing.

My father, John A. O’Keefe, III, NASA scientist, made his bones studying the variability of R Corona Borealis. I had never realized, or paid attention to, the fact that Harvard had been doing variable stars since the 1870’s when Henry Draper, who pioneered using photography with a telescope, died, and his widow funded studies at Harvard as a monument to her husband’s memory. 

In the 1800’s lots of institutions of higher learning had telescopes. Places like Harvard and Vassar had not yet been overtaken by nightly light pollution, and the size of a good and useful telescope didn’t dwarf available real estate. In fact, Sobel writes that quite a few ladies had telescopes and the head of Harvard Observatory, Edward Pickering, appealed to them to do some observations for him, particularly assigning them specific variable stars to record through time. Crowd sourcing has a long pedigree. Who knew?!

The first step in studying stars is to describe their location, brightness, and color. This operation became steadily more important as telescopes pushed the limits of what could be seen. Stars up to magnitude 6 are visible to the unaided human eye. ‘Down’ to magnitude 6 might be more appropriate, since 6 is fainter than 1. In a very dark area and especially at higher altitudes, stars of magnitude 7 can be seen occasionally. With the telescopes available at the end of the 1800’s starts up to magnitude 14 were visible, and all those new stars had to be catalogued. All the same, when this is done — what next?! 

Pickering, head of the Harvard Observatory had several answers for that. 

Initially, the brightness of stars was a very subjective observation. Pickering changed that by inventing various ways to compare brightness to a standard that could be used widely. The unexpected result of this super careful measurement of brightness (or magnitude) was the realization that the brightness of some stars varied. Women didn’t generally get to use the telescopes at night. Instead during the day, they studied the pictures that had been taken and catalogued minute changes. After some mind-numbingly tedious work, often done in pairs, with one woman making her observation from a photographic plate and another writing down what she said, real variability in star brightness was demonstrated. Also, variations in the variability were documented. Some stars varied over days, some over years. 

Henry Draper’s photos had been taken with a prism in the telescope. These pictures showed Fraunhofer lines, dark bands across the rainbow produced by passing the starlight through a prism. These bands in spectra had been noticed years earlier by Joseph von Fraunhofer. Draper concentrated on the spectrum of a single star in his photography. The Observatory found a way to place a prism in the telescope such that every star in a photo had its own spectral signature. The incredibly tedious and yet vitally important work of studying these photos and cataloguing the information brought out this way, was done by the women Pickering hired. Hence, they were the first to make the connection between variability and the Fraunhofer lines. They found binary stars this way. When it was realized that the Fraunhofer lines showed the chemistry of different stars, they already knew which stars shared the same lines and therefore the same chemistry. They classified the stars in several different ways from their work. These classifications, made on the basis of observable characteristics, turned out to have implications for star temperatures, and star evolution. Particularly important women include Annie Jump Cannon, Williamina Fleming, Antonia Maury, and Henrietta Leavitt. 

Having reread Dava Sobel’s book, I understand R Corona Borealis, my father’s star, much better. Its magnitude varies in a somewhat random way so that it isn’t a binary, for example. Those have very regular magnitude changes, and their Fraunhofer lines can reveal the chemistry of slightly different stars, helping to prove the star pairing. The hypothesis my father came to was that R Corona was a late stage star, with a lot of carbon being ejected. Periodically the carbon condensed and blotted out the light of the star. Then when it had been blown away into space R Corona brightened again. 

The Glass Universe describes Pickering’s tenure as head of the Harvard Observatory and then continues with Harlow Shapley. I’m conditioned to dislike Shapley because he wouldn’t let my father continue graduate studies at Harvard, but it did seem to me that he was much more interested in credentials than Pickering had been. Shapley lost his Great Debate because he trusted a friend instead of checking data. He didn’t really help Cecilia Payne-Gaposhkin when she discovered that hydrogen and helium were the most abundant elements in the universe. However, the contrast between the two men makes the book more fascinating. 

https://wordpress.com/post/catholicfictioncatholicscience.com/2998  This link describes a bit more about John O’Keefe. 

https://catholicfictioncatholicscience.com/2023/09/22/people-my-father-knew/ This post describes the Great Debate that Shapley basically lost about the size of the Milky Way and the Universe in general.