Dutch astronomer, pioneer in radio astronomy, comet and galaxy exploration. Oort showed that our sun is not at the centre of Universe, but just a star in the rotating Milky Way, one rotating galaxy between many others.
Jan Oort was the second child of the psychiatrist Abraham Hermanus Oort (28 March 1869, Harlingen – 12 May 1941, Leiden) and Ruth Hannah Faber (6 October 1869, Ossendrecht – 20 November 1957, Leiden), who married 14 September 1897 at Leiden and got five children. Both parents came from a family of pastors and theologians. The philologist, Orientalist and theologian Henricus Oort (27 December 1836, Eemnes – 13 December 1927, Leiden) was his grandfather.
When Oort was born his father worked in the psychiatric hospital of Franeker. At age 3, on 27 May 1903 his father got a job at the Rhijngeest Psychiatric Clinic in Oegstgeest. Here the family lived in the directors house of the clinic between the woods. Oort attended the primary school in Oegstgeest and the HBS in Leiden.
In 1917 he went to Groningen University, to study astronomy under the famous Jacobus Cornelius Kapteyn (19 Jan 1851, Barneveld – 18 June 1922, Amsterdam). He first doubted between physics and astronomy, but after his “Kandidaats” exam (2 July 1919) he got involved in the milky way research of Kapteyn. Kapteyn discovered in 1904 (in Leiden, as Groningen had not an astronomy observatory) the two main streams of stars that appear to be moving in opposite directions using spectroscopy and influenced both the empiricist Oort and the theorist Lindblad.
Jan Oort graduated 5 November 1921 cum laude. He worked here as an assistant of Kapteyns sucessor professor P.J. van Rhijn for a year and then studied from 1922 to 1924 at the observatory of the Yale University in Connecticut. He worked the positioning of start near to the sun, and had an interests in high velocity stars that did not fit the models.
When Oort came back from the US, professor Willem de Sitter, also a student of Kapteyn invited him to work as an astronomer at the Leiden Observatory. Oort became director of it from 1945 to 1970. He finished his investigations and received his doctorate 1 May 1926 (16h00) in Groningen cum laude under Van Rhijn with the thesis “The stars of high velocity”.
Oort was not satisfied with his thesis, as he could not give an explanation for the fast moving stars. Till then, the star world was seen as basically a resting system, but in 1926 the great Swedish astronomer Bertil Lindblad (26 Nov 1895, Örebro, 25 June 1965, Saltsjöbaden) postulated an alternative model of the milky way as a rotating disc with the sun being relatively far away from the centre (“the theory of the rotation of galaxies”). Stars near the centre would be the fast moving stars (compare with the fast moving planets Mercury and Venus near the sun). In two articles in 1927 and 1928 Jan Oort empirically confirmed Lindblad’s intuitive (sic) deduction and established his reputation as an influential astronomer.
Oort became conservator in 1926, lector in 1930 at Leiden University. He got invitations from Harvard and Columbia University, but refused them. Oort became professor of astronomy at the University of Leiden from 1935 to 1970. His first lecture (15 november 1935) “De bouw der sterrenstelsels” (The build of starry constellations) became his program for the rest of his live. He had many connections being the general secretary of the International Astronomical Union from 1935 to 1948 and from 1958 to 1961 being president of it.
During the war, in May 1942 the very principal Oort resigned from Leiden University, as he did not want to sign the “loyaliteitsverklaring” with the German occupants. He was very angry about the dismissal by the Germans of Eduard Maurits Meijers (January 10, 1880 10 AM, Den Helder – June 25, 1954 in Leiden), the jurist of Jewish background who was the founding father of the current Dutch civil code. To prevent from being taken hostage in Camp Vught, as happened to so many opposing the Germans Dutch professors, he and his family fled to the small village Hulshorst. The Germans used the strategy of executing prominent kept in hostage Dutchmen when a German soldier was shot by the Dutch resistance. In exile, in Hulshost, he began writing a book on stellar dynamics.
During the war (1944) he was stimulated by then student at Utrecht, later famous Dutch astronomer and mathematician in Leiden, Hendrik van de Hulst (19 November 1918 – 31 July 2000) to set up a radio-astronomy project to detect the 21-centimeter radio emission from interstellar hydrogen. Till then stars were observed with telescopes. Lenses and prisms were used to spectroscopically analyse the light. But stars emit much more frequencies than that of the spectrum of visible light.
Karl Guthe Jansky (22 October 1905 – 14 February 1950) already had “serendipitously” discovered at Bells Lab the first astronomical radio source in 1933. A great advantage of radio astronomy is that the astronomer does not need to spent the whole night way from home in the hope of a clear sky at the observatory – not likely in the Lowlands and spoiled by light city of Leiden – for doing observations. But radio astronomers can use band tapes to record it, and analyse the data afterwards.
After the war Oort led the Dutch radio astronomy group that set up radio telescopes at Kootwijk, Dwingeloo and Westerbork, using of the radar equipment that was left behind by the Germans on the coast of Holland, that were then owned by the Dutch Postal Service (PTT). Oort used the radio telescopes to record the 21-centimeter Hydrogen line to map the Milky Way, including the large-scale spiral structure, the galactic center, and gas cloud motions.
In 1959 Oort postulated a vast cloud of small bodies in an orbit about one light year away from the sun (“Oort cloud”) as the origin of comets.
He died at age 92 on 5 November 1992 in Leiden. Nobel Prize winning astrophysicist Subrahmanyan Chandrasekhar remarked, “The great oak of Astronomy has been felled, and we are lost without its shadow.”
Personal
He married on 24 May 1927 in Utrecht Johanna Maria Graadt van Roggen (7 January 1906, Nijmegen -1993), a poet. They got 2 sons and a daughter Marijke Oort (25 April 1931, Leiden – 19 December 2008, Haarlem ).
His son Coenraad Jan (Coen) Oort (5 December 1928, Leiden – 23 November 2007, Wassenaar) became a professor in economy and top Dutch civil servant from 1971-1977: “Thesaurier-generaal” (Treasurer). He was in charge of the “Oort commission” that reformed the Dutch tax system in 1990.
His son Abraham H. Oort (?, Leiden – ) studied physics and became a climatologist at the Geophysical Fluid Dynamics Laboratory of the National Oceanic and atmospheric Administration at Princeton University, New Jersey. He and Jose P. Peixoto published on 1 February 1992 the handbook “Physics of Climate”. After thirty years of scientific work he became a sculptor and Shiatsu therapist. Source: “Intuitive astrology” by Elisabeth Rose Campbell, who not only describes his horoscope, but also his commentary on it. We read on http://www.atasteofhealth.org: “Abraham has a private practice in Shiatsu and CranioSacral Therapy in Hartland, VT. He practices mindfulness meditation as a student of the Vietnamese Zen Master Thich Nhat Hanh. He has further been initiated as a Oneness Blessing Facilitator at the Oneness University, Chennai, India.”
The astronomer Jan Oort (“oort/oord” means “locality, space, place”) was a declared enemy of astrology. But his son, the climatologist Abraham was certainly not. Jan Oort liked ice skating and kept records of his skating opportunities. He was the steering man of the Groningen students’ rowing team (c. 1920). He liked art, like his wife, strolling in nature and always visited museums when being abroad.

Link to Wikipedia