Our Galaxy is Not Alone, 1925|
JF Ptak Science Books Post 2027
I was about to post this great image of the attendees of a significant meeting of the American Astronomical Society taken during the meeting in D.C. over New Year's 1924 (Dec 30 1924-January 1, 1925--certainly no one for many years has thought about holding a professional meeting on such a date!1) but I cannot let it pass that the paper on the other side of the photo was one of very high importance.
First, the photo, which I have not yet been able to locate easily online:
[More detailed closeups are available in the continued reading section, below. Source: Popular Astronomy, volume 33, April, 1925.]
The paper directly opposite the slick reverse of the photo spread is Edwin Hubble's "Cepheids in the Spiral Nebulae"--it was reported in the issue of Popular Astronomy for the 1924 meeting, though Hubble himself wasn't actually there. No matter--he was a meticulous and methodical man, and it seems he was at odd in pressing his results into print too quickly because it contradicted established thinking, which called for caution. (The results of his findings had been earlier presented in the New York Times in November 19242.) But the paper--to paraphrase my brother-in-law Mickey Digh--"was what it was", and (using Shapley's calibration for the period-luminosity relation, published in the Astrophysical Journal in 1918) announced the discovery of Cepheid variable stars in the nebulae M 31 and M 33, placing them at vast distances, well outside our galaxy. This in effect established that the belief of our galaxy being the only galaxy in he universe was incorrect, and that the Great Debate arguing these points on the nature of the nebulae and begun decades earlier was settled.
In the next year, 1926, Hubble would contribute a paper on the classification of the nebulae ("Extra-galactic Nebulae", in the Astrophysical Journal, volume 64, pp 321-369) which was highly adaptable and proved to be iconic. Three years later, continuing on the theme of the 1925 paper, Hubble published what has been seen by many as the great astronomical paper of the century, the 1929 Velocity-distance relationship, with Hubble's Constant. So not only were there galaxies existing outside of our own as he had demonstrated in 1925, but that these galaxies were moving, and quickly, away from each other, everywhere. This was the establishment of the expanding universe--the Big Bang stuff (famously put forward in the April 1 Alpher-Bethe-Gamow paper by Alpher, Gamow and Herman but no Bethe, a bit of nerd humor to get ABC out of the initials of the authors of the paper on April Fool's Day, 1939) would come about to explain what the 1929 paper established.
Anyway, the 1925 paper is a major step in the history of cosmology, and perhaps the greatest effort in observational cosmology of the 20th century.
1. I must admit, poor suffering reader, that this writer managed to once schedule a meeting of a microscopical and scientific instrument society swap/one-day meeting on Mother's Day, years ago. Not good.
2. The results of Hubble's work had been widely distributed among astronomers prior to the reading of the paper on 1 January 1925 at the meeting, this according to Lang and Gingerich in the great A Source Book in Astronomy and Astrophysics, 1900-1975, page 713, and also Michael Crowe, Modern Theories of the Universe, from Herschel to Hubble, page 336. Also see the work by R.Berendzen and M.Hoskin "Hubble's Announcement of Cepheids in Spiral Nebulae", 1971, here.