Jan Oort

Jan Oort
Born	28 April 1900(1900-04-28) Franeker, Friesland
Died	5 November 1992(1992-11-05) (aged 92) Leiden
Nationality	Dutch
Fields	Astronomy
Doctoral advisor	Jacobus Cornelius Kapteyn
Known for	Oort cloud

Jan Hendrik Oort (Franeker, 28 April 1900 – Leiden, 5 November 1992) was a Dutch astronomer. He was a pioneer in the field of radio astronomy. The Oort cloud of comets bears his name.

Oort was born in Franeker, Friesland and studied in Groningen with Jacobus Cornelius Kapteyn. His Ph.D thesis was titled The stars of high velocity. In 1927 he confirmed Bertil Lindblad's theory that the Milky Way galaxy rotates, by analyzing the movements of stars.^[1] In 1935 he became professor at the observatory of the University of Leiden, where Ejnar Hertzsprung was the director.

In 1928 his son Coen Oort was born, who later became an important Dutch economist and public official and who in 1990 headed the Oort Commission, which was responsible for a major overturn of Dutch tax law.

Oort was fascinated by radio waves from the universe. After the Second World War he began work in the new field of radio astronomy, using an old radar antenna from the Germans.

In the 1950s he raised funds for a new radio telescope in Dwingeloo, in the east part of the Netherlands, to research the center of the galaxy. In 1970 a bigger telescope (the Westerbork Synthesis Radio Telescope) was built in Westerbork, near the old one. It consisted of twelve smaller telescopes working together to perform radio interferometry observations, a technique which had been previously suggested by Oort, but which was first tested experimentally in Cambridge by Martin Ryle and in Sydney by Joseph Pawsey.

His hypothesis that the comets have a common origin, postulated in 1950, was later proven to be incorrect in detail, though correct in principle. That is, different types of comets have origins in different regions of the outer solar system. For more, see Oort Cloud, Hills Cloud, and Kuiper Belt. Another contribution Oort made was to demonstrate that the light from the Crab nebula was polarized.

A few of Oort's discoveries

• In 1924, Oort discovered the galactic halo, a group of stars orbiting the Milky Way but outside the main disk.^[2]
• In 1927, he calculated that the center of the Milky Way was 5,900 parsecs (19,200 light years) from the Earth in the direction of the constellation Sagittarius.^[1]
• He showed that the Milky Way had a mass 100 billion times that of the Sun.
• In 1950 he suggested that comets came from a common region of the Solar System (now called the Oort cloud).
• He found that the light from the Crab Nebula was polarized, and produced by synchrotron emission.

Honors

Commemorative plate at the house where Jan Oort was born in Franeker.

Awards

• Bruce Medal of the Astronomical Society of the Pacific in 1942
• Gold Medal of the Royal Astronomical Society in 1946
• Henry Norris Russell Lectureship of the American Astronomical Society in 1951
• Gouden Ganzeveer in 1960
• Karl Schwarzschild Medal of the Astronomische Gesellschaft in 1972
• Balzan Prize for Astrophysics in 1984

Named after him

• Asteroid 1691 Oort
• Oort Cloud
• Oort constants of galactic structure

Upon his death, Nobel Prize Subrahmanyan Chandrasekhar remarked, "The great oak of Astronomy has been felled, and we are lost without its shadow."^[3]

References

Notes

1. ^ ^{a b} J. H. Oort (1927-04-14), "Observational evidence confirming Lindblad's hypothesis of a rotation of the galactic system", Bulletin of the Astronomical Institutes of the Netherlands 3 (120): 275–282, Bibcode 1927BAN.....3..275O. 
2. ^ J. H. Oort; Arias, B; Rojo, M; Massa, M (June 1924), "On a Possible Relation between Globular Clusters and Stars of High Velocity", Proc Natl Acad Sci U S A. 10 (6): 256–260, Bibcode 1924PNAS...10..256O, doi:10.1073/pnas.10.6.256, PMC 1085635, PMID 16586938, http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1085635. 
3. ^ van de Hulst, H. C. (1994), "Jan Hendrik Oort (1900–1992)", Quarterly Journal of the Royal Astronomical Society 35 (2): 237–242, Bibcode 1994QJRAS..35..237V. 

Literature

• Oort, JH (1970), "Galaxies and the Universe: Properties of the universe are revealed by the rotation of galaxies and their distribution in space", Science 170 (3965): 1363–1370, 1970 Dec 25, Bibcode 1970Sci...170.1363O, doi:10.1126/science.170.3965.1363, PMID 17817459 
• Rougoor, G W; Oort, J H (1960), "DISTRIBUTION AND MOTION OF INTERSTELLAR HYDROGEN IN THE GALACTIC SYSTEM WITH PARTICULAR REFERENCE TO THE REGION WITHIN 3 KILOPARSECS OF THE CENTER", Proc. Natl. Acad. Sci. U.S.A. 46 (1): 1–13, 1960 Jan, Bibcode 1960PNAS...46....1R, doi:10.1073/pnas.46.1.1, PMC 284997, PMID 16590580, http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=284997 
• Oort, J H (1924), "Note on the Difference in Velocity between Absolutely Bright and Faint Stars", Proc. Natl. Acad. Sci. U.S.A. 10 (6): 253–6, 1924 Jun, Bibcode 1924PNAS...10..253O, doi:10.1073/pnas.10.6.253, PMC 1085634, PMID 16586937, http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1085634 

Online exhibition

Jan Oort, astronomer (Leiden University Library, April–May 2000) [1]

Persondata
Name	Oort, Jan
Alternative names
Short description
Date of birth	28 April 1900
Place of birth	Franeker, Friesland
Date of death	5 November 1992
Place of death	Leiden