Relations Between the Spectra and Other Characteristics of the Stars. Offprint from Popular Astronomy, Vol. 22, Nos. 5 – 6, 1914.

[Northfield, Minnesota: Goodsell Observatory of Carleton College, 1914].

First edition, extremely rare separately-paginated offprint, of this classic paper describing the Hertzsprung-Russell diagram. “During his first years on the Princeton faculty, Russell’s analysis of his trigonometric parallax data led him to discover, contemporaneously with, but independently of, Danish astronomer Ejnar Hertzsprung, the correlation between a star’s intrinsic brightness and its spectral type. Hertzsprung was the first to work out a diagram showing the relationship between temperature and luminosity for a group of stars (1911/1912), but few astronomers came across its publication in a photographic journal. When Russell plotted his diagram in late 1913, leading to the publication of the Hertzsprung-Russell diagram the following year [offered here], it had an enormous effect on the scientific community. The diagram remains one of the most important in astrophysics” (Biographical Encyclopedia of Astronomers). The paper was published in two parts, pp. 275-294 in Vol. 22, No. 5 and pp. 331-350 in No. 6. Both parts are contained in this separately-paginated offprint. OCLC locates a single copy, at the University of Chicago. No copies in auction records.

Provenance: Richard Prager (1883-1945), German-American astronomer (name stamp on front wrapper). “Prager was born in Hannover, Germany. He became an assistant in the German Academy of Sciences in 1908. The following year he became head of the Observatorio Nacional in Santiago, Chile, where he remained until 1913. He then returned to Berlin, becoming an observer at the Berlin-Babelsberg Observatory. In 1916 he became a professor. He was an early pioneer of stellar photoelectric photometry. He is noted for his work in the field of variable stars, and he made numerous contributions to Astronomische Nachrichten on this topic. In 1938 he was imprisoned by the German Nazis. His friends in England obtained his release in 1939, and he moved to the United States where he accepted a position at the Harvard Observatory. However, his health had suffered from his imprisonment and from his separation from his family, and he died only six years later. The crater Prager on the Moon is named in his honor” (Wikipedia, accessed 6 August 2017).

“Studying the spectra of stars classified by spectral type by Antonia Maury at the Harvard College Observatory, Hertzsprung between 1906 and 1909 commented on relations between brightness and spectral type. Little note was taken of this work, however, until Russell forcefully presented the material in a lecture at a joint meeting of the American Association for the Advancement of Science and the Astronomical and Astrophysical Society in 1913 and then in a paper published in 1914. Russell had much more data than Hertzsprung had had five years earlier, and the case for a relation between absolute magnitude and spectral class was correspondingly more convincing.

“Russell began his classic paper by noting that “investigations into the nature of the stars must necessarily be very largely based upon the average characteristics of groups of stars selected in various ways – as by brightness, proper motion, and the like. The publication within the last few years of a great wealth of accumulated observational material makes the compilation of such data an easy process; but some methods of grouping appear to bring out much more definite and interesting relations than others, and, of all the principles of division, that which separates the stars according to their spectral types has revealed the most remarkable differences and those which most stimulate attempts at a theoretical explanation.”

“He went on to state that that the possibility of obtaining with an objective prism photographs of spectra of hundreds of stars on a single plate had resulted in over 100,000 classified spectra of stars and some interesting conclusions. “The spectra of the stars show remarkably few radical differences in type. More than ninety-nine per cent of them fall into one or other of the six great groups which, during the classic work of the Harvard College Observatory, were recognized as of fundamental importance, and received as designations, by the process of ‘survival of the fittest’, the rather arbitrary series of letters B, A, F, G, K, and M. That there should be so few types is noteworthy; but much more remarkable is the fact that they form a continuous series.”

“Russell’s primary concern was to identify the predominant cause of the spectral differences, which he attributed to differences in temperature. Also in his classic paper he rapidly reviewed some of the relations brought to light between other characteristics of the stars and their spectral types, and then discussed in more detail the relations between spectra and brightness. Hertzsprung and others had already discussed this issue, and many of the facts presented by Russell were not new. But his material was much more extensive than any hitherto assembled. There were direct trigonometric parallaxes for a few stars, and average proper motions and thus average parallaxes or distances for many others. Russell assembled data from many astronomical studies. Using approximately 300 stars whose distances had been directly measured by 1913, and another 150 stars in four clusters with well-known distances, Russell found that graphs of absolute magnitude and spectral type produced a rapidly descending diagonal line from B to M and another, almost horizontal line, starting at B and running to M. Had he had thousands of stars rather than hundreds, and had he been able to plot their absolute magnitudes without the uncertainty arising from observational errors and from using averages of distances, the data points very likely would lie even closer together. There were two great classes of stars: (1) the giant stars, about 100 times as bright as the sun and varying little with spectral type, and (2) the dwarf stars, of smaller brightness and falling off rapidly with increasing redness.

“With giant and dwarf stars differentiated, Russell went on to ask in his classic paper what in the nature of their constitutions gave rise to the differences in brightness and why did the differences show a systematic increase with spectral type. This investigation took him into the issue of a possible correlation between mass and luminosity and into the more general problem of stellar evolution. The paper was remarkable both in its range and its depth. Much that Russell said would bear revision, but he had set an agenda for others to follow, in stellar evolution and in outlining for further study and refinement what would in future be referred to as the Hertzsprung-Russell diagram” (Hetherington (ed.), Routledge Encyclopedia of Cosmology, pp. 278-280).

8vo (245 x 158 mm), pp. [1], 2-40. Stapled as issued in original printed wrappers. Spine rubbed, staplles rusted.

Item #4323

Price: $1,800.00

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