Who wrote the the best astrophysics thesis ever? There must be several contenders: for precociousness, it’s hard to beat Frank Shu’s undergraduate thesis explaining why galaxies have spiral arms, and Dave Charbonneau’s “Shadows and Reflections of Extrasolar Planets” must be right up there among top doctoral theses.
But Otto Struve had a hard-to-argue with nomination. I’ll let Rob Rutten explain the context of the classification of stellar spectra at Harvard in the early 1900’s:
A sequence of women, most of them hired as “computers”, developed the classification scheme.
The first, Williamina Fleming, did most of the work for the Draper Memorial of 10,351 stars. She classified them in a scheme assigning different letters to different types… she later revised the scheme when the element helium and its lines were identified.Antonia Maury, a niece of Henry Draper, was the next… She came up with a new classification scheme, in twenty-two classes plus five orthogonal divisions…Annie Cannon (1863-1941) who “must rank among the most dedicated of astronomers of all time and certainly as one of the most illustrious from the female ranks” (Hearnshaw 1986)… updated Fleming’s original classification scheme by accounting for ionized helium lines… Miss Cannon constructed the O-B-A-F-G-K-M sequence with decimal subdivisions that is still in use… After taking part in classifying some 5000 bright stars, she started on the Henry Draper Catalogue, the successor to the Henry Draper Memorial, in 1911 and completed the classification of 225,300 stars within four years, at an average of 30 per working hour. She had assistants but must indeed have worked diligently. Her lifetime total amounts to 395,000 classifications.
This is a stunning amount of work, and Annie Cannon’s accomplishment is rightfully regarded as a turning point in astronomy. But Miss Cannon did not earn a PhD for this work; she was a “mere” “computer”. And this was all still phenomenological: no one understood why the OBAFGKM sequence existed, and they assumed it was evolutionary. We still call cool stars “late-type” because of this misconception. But then, slowly, physics started to catch up to observation. Back to Rutten, discussing the mystery of stellar spectral types:
That puzzle was solved after the influence of pressure had been recognized by Pannekoek, Saha had produced his equation for ionization equilibria, and Fowler and Milne had connected stellar colors with ionization differences.
The crown came with the 1925 thesis of Cecilia Payne, the first woman to obtain an astronomy PhD at Harvard, which was later called “undoubtedly the most brilliant PhD thesis ever written in astronomy” by Struve. She showed that all stars more or less share the same composition, but display different line strengths from Saha-Boltzmann sensitivities to temperature and density. Stellar spectroscopy had matured from morphology to astrophysics.
It’s hard to beat inventing the field of stellar astrophysics. I think Struve’s assessment still stands.
Two last connections: Among Cecilia Payne’s PhD students later in life was Dr. Frank Kameny, the most famous astronomer most astronomers have never heard of. Finally, a great breakdown of how important her work is for us today is illustrated by this PhD Comics video, starring none other than AstroWright close friend and collaborator John Asher Johnson and his Exolab:
Update: I should cite some things here. The image of the at the top of “Pickering’s Harem” (as the “Harvard Computers” were less-than-respectfully known) is from Rob Rutten’s excellent class notes on Stellar Atmospheres, which you can find if you follow the link. Rob cites Hearnshaw, J. B.: 1986, The analysis of starlight. One hundred and fifty years of astronomical spectroscopy, Cambridge Univ. Press, Cambridge UK. According to this page the photo was found in an album that belonged to Annie Cannon. Pickering is the man, and among the women the only one mentioned in this blog entry is Annie herself, standing tall two people to Pickering’s left (just right of center).
I grabbed the image of Cecilia Payne-Gaposchkin at her desk from Wikipedia, it but originates from the Smithsonian Flickr stream (Acc. 90-105 – Science Service, Records, 1920s-1970s, Smithsonian Institution Archives).
Update 2: Ryan Chornock points out another strong contender: Russell Hulse, for the Nobel-Prize-winning discovery of binary pulsar B1913+16, which eventually proved the existence of gravity waves and provided the tightest constraint on strong GR. Winning a Nobel for your graduate work automatically gets you on the list, I’d say, which means that Jocelyn Bell should be on this list, too (though the prize went to her adviser).