Trumpler, Robert J.


Renowned American astronomer, studied and classified open clusters; craters on the Moon and Mars named for him



Type: Signed card

Description: (1886-1956) Swiss-born American astronomer, earned 1910 Ph. D. from the Universitat Zurich. To the US in 1915 citizen 1921, joined the University of California taking a position at Allegheny Observatory, later to Lick Observatory. He was elected a member of the US National Academy of Sciences 1932.

He is most noted for observing that the brightness of the more distant open clusters was lower than expected, and the stars appeared more red. This was explained by the interstellar dust scattered through the galaxy, resulting in the absorption (extinction) of light or interstellar extinction of light. Trumpler further studied and catalogued open clusters to determine the size of the Milky Way galaxy. At first he thought his analysis placed an upper limit on the Milky Way’s diameter of about 10,000 parsecs with the Sun located somewhat near the center although he later revised this. While cataloguing open clusters, he also devised a system for their classification according to the number of stars observed within them, how concentrated these stars are in the center of the cluster and the range of their apparent brightness. This system, the “Trumpler classification”, is still in use today.

The Astronomical Society of the Pacific awards the Robert J. Trumpler Award for an outstanding PhD Thesis in astronomy. A crater on the Moon and on Mars are named for him as well as 6 open clusters, incl. Trumpler 14, an open cluster in the Carina constellation.

Signed 2 x 3 ½ card, adds Aptos, Calif., December 27 1951.

Condition: Very Good 



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