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:
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.
The other odd thing about this issue is that contains another "first"--not as significant as the Hubble, but still very interesting. It is a short paper by L.J. Comrie--an early visionary and practicioner of the use of the calculator and computer--on the application of the electric calculator to solving problems in astronomy. It looks like this may be the first paper on the use of the electric calculator to solve complex computation problems in astronomical issues. If this isn't the first paper on the subject, it is close to being so--I haven't yet figured that out.