Robert Julius Trumpler (until 1915 Robert Trümpler, born October 2, 1886 in

Zürich , neighboring_municipalities = Adliswil, Dübendorf, Fällanden, Kilchberg, Maur, Oberengstringen, Opfikon, Regensdorf, Rümlang, Schlieren, Stallikon, Uitikon, Urdorf, Wallisellen, Zollikon , twintowns = Kunming, San Francisco Zürich ...

, Switzerland; died September 10, 1956 in

Berkeley Berkeley most often refers to: *Berkeley, California, a city in the United States **University of California, Berkeley, a public university in Berkeley, California * George Berkeley (1685–1753), Anglo-Irish philosopher Berkeley may also refer ...

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...

) was a Swiss-

American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the "United States" or "America" ** Americans, citizens and nationals of the United States of America ** American ancestry, pe ...

astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either ...

Career

After initial schooling, Trumpler entered the

Universität Zürich The University of Zürich (UZH, german: Universität Zürich) is a public research university located in the city of Zürich, Switzerland. It is the largest university in Switzerland, with its 28,000 enrolled students. It was founded in 1833 f ...

but later transferred to the

University of Göttingen The University of Göttingen, officially the Georg August University of Göttingen, (german: Georg-August-Universität Göttingen, known informally as Georgia Augusta) is a public research university in the city of Göttingen, Germany. Founded ...

where he earned his PhD in 1910. In 1915, during

World War I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...

, he emigrated to the

and joined the

University of California The University of California (UC) is a public land-grant research university system in the U.S. state of California. The system is composed of the campuses at Berkeley, Davis, Irvine, Los Angeles, Merced, Riverside, San Diego, San Franci ...

. He took a position at

Allegheny Observatory The Allegheny Observatory is an American astronomical research institution, a part of the Department of Physics and Astronomy at the University of Pittsburgh. The facility is listed on the National Register of Historic Places (ref. # 79002157, ad ...

, and later went to Lick Observatory. In 1921, he became a

naturalized citizen Naturalization (or naturalisation) is the legal act or process by which a non-citizen of a country may acquire citizenship or nationality of that country. It may be done automatically by a statute, i.e., without any effort on the part of the in ...

of the United States. He was elected a member of the

United States National Academy of Sciences The National Academy of Sciences (NAS) is a United States nonprofit, non-governmental organization. NAS is part of the National Academies of Sciences, Engineering, and Medicine, along with the National Academy of Engineering (NAE) and the Nati ...

in 1932. He is most noted for observing that the brightness of the more distant

open cluster An open cluster is a type of star cluster made of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, an ...

s was lower than expected, and the stars appeared more red. This was explained by the

interstellar dust Cosmic dust, also called extraterrestrial dust, star dust or space dust, is dust which exists in outer space, or has fallen on Earth. Most cosmic dust particles measure between a few molecules and 0.1 mm (100 micrometers). Larger particles are c ...

scattered through the galaxy, resulting in the absorption (extinction) of light or

interstellar extinction In astronomy, extinction is the absorption and scattering of electromagnetic radiation by dust and gas between an emitting astronomical object and the observer. Interstellar extinction was first documented as such in 1930 by Robert Julius Trump ...

of light. Trumpler further studied and catalogued open clusters in order to determine the size of the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...

galaxy. At first he thought his analysis placed an upper limit on the Milky Way's diameter of about 10,000

parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, an ...

s with the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

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, known as the '' Trumpler classification'', is still in use today.

Honors

The Robert J. Trumpler Award, awarded by the Astronomical Society of the Pacific for an outstanding PhD Thesis in astronomy, is named in his honor.Robert J. Trumpler Award for an Outstanding PhD Thesis.
Astronomical Society of the Pacific. Accessed September 7, 2008. ''The following celestial features are named after him:'' * The crater Trumpler on the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

. * Trumpler Crater on

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...

. * ''Trumpler classification'', the classification scheme for

s. * ''Trumpler catalogue'', the catalogue of open clusters that he compiled.

Notable objects

Some notable objects from his 1930 catalogue of open clusters are: * Trumpler 2 *

Trumpler 14 Trumpler 14 (''Tr 14'') is an open cluster with a diameter of , located within the inner regions of the Carina Nebula, approximately from Earth. Together with the nearby Trumpler 16, they are the main clusters of the Carina OB1 stellar associa ...

* Trumpler 15 *

Trumpler 16 Trumpler 16 (''Tr 16'') is a massive open cluster that is home to some of the most luminous stars in the Milky Way galaxy. It is situated within the Carina Nebula complex in the Carina–Sagittarius Arm, located approximately from Earth. The cl ...

* Trumpler 27

Selected publications

* R.J. Trumpler, 1930. "Preliminary results on the distances, dimensions and space distribution of open star clusters." ''Lick Obs. Bull''. Vol XIV, No. 420 (1930) 154-188. Table 16 is the Trumpler catalog of open clusters, referred to as "Trumpler (or Tr) 1-37 * Robert Julius Trumpler, Harold F. Weaver 1962. ''Statistical Astronomy'' (Dover Publications, New York). (reprinted from original published by the University of California, Berkeley, 1953)

References

National Academy of Sciences biography - Biographical Memoirs V.78 (2000)
pp. 276–297

* ttp://spiff.rit.edu/classes/phys230/lectures/ism_dust/ism_dust.html The Interstellar Medium: Dust *

Career

Honors

Notable objects

Selected publications

See also

References

Further reading