Robert Julius Trumpler (October 2, 1886 – September 10, 1956) was a Swiss-American

astronomer An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth. Astronomers observe astronomical objects, such as stars, planets, natural satellite, moons, comets and galaxy, galax ...

Career

Born in

Switzerland Switzerland, officially the Swiss Confederation, is a landlocked country located in west-central Europe. It is bordered by Italy to the south, France to the west, Germany to the north, and Austria and Liechtenstein to the east. Switzerland ...

in October 2, 1886, where Trumpler did initial schooling. Trumpler entered the Universität Zürich but later transferred to the

University of Göttingen The University of Göttingen, officially the Georg August University of Göttingen (, commonly referred to as Georgia Augusta), is a Public university, public research university in the city of Göttingen, Lower Saxony, Germany. Founded in 1734 ...

where he earned his

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in 1910. In 1915, during

World War I World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...

, he emigrated to the

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and joined the

University of California The University of California (UC) is a public university, public Land-grant university, land-grant research university, research university system in the U.S. state of California. Headquartered in Oakland, California, Oakland, the system is co ...

. He took a position at Allegheny Observatory, and later went to

Lick Observatory The Lick Observatory is an astronomical observatory owned and operated by the University of California. It is on the summit of Mount Hamilton (California), Mount Hamilton, in the Diablo Range just east of San Jose, California, United States. The ...

. In 1921, he became a

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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 tens 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, and ...

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

interstellar dust Cosmic dustalso called extraterrestrial dust, space dust, or star dustis dust that occurs in outer space or has fallen onto Earth. Most cosmic dust particles measure between a few molecules and , such as micrometeoroids (30 μm). Cosmic dust can ...

scattered through the

galaxy A galaxy is a Physical system, system of stars, stellar remnants, interstellar medium, interstellar gas, cosmic dust, dust, and dark matter bound together by gravity. The word is derived from the Ancient Greek, Greek ' (), literally 'milky', ...

, resulting in the absorption (extinction) of light or interstellar extinction of light. Trumpler further studied and catalogued open clusters in order to determine the size of the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

. 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, and ...

s with the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

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 Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

. * Trumpler Crater on

Mars Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...

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

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

Trumpler Classification for open star clusters

Trumpler's classification method for

open star clusters Open or OPEN may refer to: Music * Open (band), Australian pop/rock band * The Open (band), English indie rock band * Open (Blues Image album), ''Open'' (Blues Image album), 1969 * Open (Gerd Dudek, Buschi Niebergall, and Edward Vesala album), ' ...

is still currently in use by astronomers. It classifies the star cluster according to three features: Degree of concentration, range of magnitude (brightness) for the stars found in the cluster and the number of stars in the cluster. Degree of concentration is given a number from 1 to 4 in

Roman numerals Roman numerals are a numeral system that originated in ancient Rome and remained the usual way of writing numbers throughout Europe well into the Late Middle Ages. Numbers are written with combinations of letters from the Latin alphabet, eac ...

(number I indicating a strong central concentration, II indicating little central concentration, III indicates no noticeable concentration and IV little difference from the surrounding stellar population). Range of magnitude is classified in a scale 1 to 3 and is written in

Arabic numerals The ten Arabic numerals (0, 1, 2, 3, 4, 5, 6, 7, 8, and 9) are the most commonly used symbols for writing numbers. The term often also implies a positional notation number with a decimal base, in particular when contrasted with Roman numera ...

. Number 1 indicates most stars within the cluster have a very similar apparent brightness. 2 indicates a medium range across the stars in the cluster and 3 indicates a significant difference in brightness, from very bright to very faint stars. The third feature classifies the number of stars inside the cluster and it uses letters. Letter '''p''' indicates a poor cluster, containing less than 50 stars. Letter '''m''' indicates a medium amount of 50 to 100 stars. Letter '''r''' indicates a rich cluster, containing more than a 100 stars. Finally, the letter '''n is attributed to all star clusters where some sort of nebulosity is present. For example, NGC 5460 is classified as a ''II3m'', an open cluster with little central concentration, significant difference in brightness among its stars and 50 to 100 stars within the cluster. Since no nebulosity is detected, the letter n is not attributed to it.

Notable objects

Some notable objects from his 1930 catalogue of open clusters are: * Trumpler 2 * Trumpler 14 * Trumpler 15 * Trumpler 16 * 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. An. 1-37 in Table 16 are Table 17 and constitute 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 *