TRUMPLER, ROBERT JULIUS

(b. Zurich, Switzerland, 2 October 1886; d. Oakland, California, 10 Septemeber 1956)

astronomy.

The third of ten children born to a Swiss industrialist, Wilhelm Ernst Trümpler, and his wife, Luise Hurter, Trumpler lived and studied in Zurich until age twenty-one. This period included two years at the University of Zurich, which he left in 1908 for the University of Göttingen; two years later he received his Ph.D. with a dissertation written under Leopold Ambronn.

Following a postdoctoral year at Göttingen, Trumpler served four years in the Swiss Geodetic Survey. He determined latitudes and longitudes, but he also became interested in the way stars in the Pleiades cluster move together across the sky. Such annual proper motions also interested Frank Schlesinger, then director of the Allegheny Observatory near Pittsburgh. He met Trumpler in 1913 at a meeting of the German Astronomical Society and invited him to come to Allegheny. Trumpler arrived in 1915 and began making comparative studies of galactic star clusters–so named because they are located in the disk of our galaxy. In August 1916 Trumpler married Augusta De La Harpe; three daughters and two sons were born to them.

At the invitation of W. W. Campbell, Trumpler went to the Lick Observatory in 1919. He joined the staff in 1920 and rose by 1929 to the post of astronomer. In 1938 he was named professor of astronomy on the Berkeley campus of the parent organization, the University of California, a position he retained until his retirement in 1951.

At Lick, Campbell chose Trumpler to assist him, in 1922, in a test of the general theory of relativity. The test involved an expedition to Wallal, on the northwest coast of Australia, to photograph stars in the sky near the totally eclipsed sun, for comparison with their positions as photographed at night four months earlier in Tahiti. The data, after suitable statistical treatment, showed an outward deflection at the edge of the sun of 1.75 ± 0.09” (compared to Einstein’s prediction of 1.745”), a result considerably more accurate than that obtained by Eddington three years earlier.

Trumpler used the thirty-six-inch Lick refractor to study Mars during the favorable opposition of 1924. To his surprise, he concluded that the long dark markings, named canals by Schiaparelli, were real–but neither as straight nor as sharp and narrow as Lowell believed them to be. Trumpler’s feeling that a”canal “such as Coprates might be a volcanic fault received some support in 1972 from close-up photographs taken by Mariner 9.

Trumpler’s work on galactic star clusters proved to be his most significant contribution. In 1925 he published evidence that the mix of stars in galactic clusters differs markedly; some clusters contain massive blue stars but no yellow or red giants, while in others the opposite is true. In the hands of later workers, such as Baade and Sandage, these findings were developed into the currently accepted picture of how individual stars evolve with time. And in 1930, in a paper including data on 334 galactic clusters, Trumpler showed that distances to galactic clusters were being overestimated because interstellar material, previously thought to be nonexistent, was dimming the starlight by an average of 0.67 magnitudes for every kiloparsec of distance. This discovery brought distances measured in the galactic disk into agreement with those found by Shapley above and below the disk, and showed why estimates of galactic size, as made for instance by Kapteyn, were too small.

Trumpler was elected to the National Academy of Sciences in 1932. The Astronomical Society of the Pacific elected him president in 1932 and again in 1939 and has established an award in his memory, given annually to a promising postdoctoral astronomer.

BIBLIOGRAPHY

I. Original Works. Trumpler’s dissertation was “Eine Methode zur photographischen Bestimmung von Merdian-durchgängen.” His work confirming the general theory of relativity appeared in two papers (both written with W. W. Campbell): Observations or the Deflection of Light in Passing Through the Sun’s Gravitional Field, Made During the Total Solar Eclipse of September 21, 1922,” in Lick Observatory Bulletin, 11 (1923), 41–54: and “Observations Made With a Pair of Five-foot Cameras on the Light Deflections in the Sun’s Gravitational Field at the Total Solar Eclipse of September 21, 1922,” 13 (1926), 130–160.

Trumpler’s study of Mars. including both photographs and drawings, can be found in “Observations of Mars at the Opposition of 1924,” ibid., 13 (1926), 19–45.

Trumpler’s first paper on galactic star clusters, “Die relativen Eigenbewegungen der Plejadensterne,” is in Astronomische Nachrichten, 200 (1915), cols. 217–230. Another early contribution, “Comparison and Classification of Star Clusters,” is in Publications of the Allegheny Observatory, university of Pittsburgh, 6 (1922), 45–74. His system for classifying galactic cluster on the basis of the spectra of their constituent stars appears in “Spectral Types in Open Clusters, in Publications of the Astronomical Society of the Pacific, 37 (1925), 307–318. His discovery of the intersellar absorption of light, including the selective way it operates, is described in “Preliminary Results on the Distances, Dimensions, and Space Distribution of Open Clusters,” in Lick Observatory Bulletin, 14 (1930), 154–188. A summary of what galactic clusters can–and cannot–reveal about intragalactic distances and galactic structure is contained in a paper Trumpler read at the dedication of the McDonald Observatory in 1939, published as “Galactic Star Clusters, “in Astrophysical Journal, 91 (1940), 186–201.

Trumpler’s book, Statistical Astronomy, written with Harold F. Weaver (Berkeley, 1953: repr., 1962), is the distillation of a graduate course he taught for over fifteen years. No complete list of Trumpler’s publications has been published. Besides the above book, he wrote nine summarizing articles and approximately sixty-five research reports.

II. Secondary Literature. An obituary notice on Trumpler, written by Harold and Paul Weaver, appeared in Publications of the Astronomical Society of the Pacific, 69 (1957), 304–307, with portrait and facs. signature.

Sally H. Dieke