Jan Oort
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Jan Hendrik Oort ( or ; 28 April 1900 – 5 November 1992) was a Dutch
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 ...
who made significant contributions to the understanding 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 ...
and who was a pioneer in the field of
radio astronomy Radio astronomy is a subfield of astronomy that studies Astronomical object, celestial objects using radio waves. It started in 1933, when Karl Jansky at Bell Telephone Laboratories reported radiation coming from the Milky Way. Subsequent observat ...
. ''
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'' called him "one of the century's foremost explorers of the universe"; the
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website describes him as "one of the greatest astronomers of the 20th century" and states that he "revolutionised astronomy through his ground-breaking discoveries." In 1955, Oort's name appeared in ''
Life Life, also known as biota, refers to matter that has biological processes, such as Cell signaling, signaling and self-sustaining processes. It is defined descriptively by the capacity for homeostasis, Structure#Biological, organisation, met ...
'' magazine's list of the 100 most famous living people. He has been described as "putting the Netherlands in the forefront of postwar astronomy". Oort determined that the Milky Way rotates and overturned the idea that 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 ...
was at its center. He also analyzed the vertical motions of stars near the Sun, using this data to estimate the local gravitational field. He calculated how much mass must be present to account for the stellar motions perpendicular to the Galactic plane. Comparing this mass to the visible stars and gas, in 1932, he wrote, "This leads to the conclusion that there must be considerable amounts of invisible matter." The following year, Fritz Zwicky called this invisible matter “dunkle Materie”, German for
dark matter In astronomy, dark matter is an invisible and hypothetical form of matter that does not interact with light or other electromagnetic radiation. Dark matter is implied by gravity, gravitational effects that cannot be explained by general relat ...
. It is now believed that dark matter makes up approximately 84.5% of the total mass in the
Universe The universe is all of space and time and their contents. It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from s ...
, and its gravitational pull is responsible for "the clustering of stars into galaxies and galaxies into connecting strings of galaxies". However, Oort's data has been challenged and his discovery may have been spurious. Oort discovered the galactic halo, a group of stars orbiting the Milky Way but outside the main disk. Additionally Oort is responsible for a number of important insights about comets, including the realization that their orbits "implied there was a lot more solar system than the region occupied by the planets." The
Oort cloud The Oort cloud (pronounced or ), sometimes called the Öpik–Oort cloud, is scientific theory, theorized to be a cloud of billions of Volatile (astrogeology), icy planetesimals surrounding the Sun at distances ranging from 2,000 to 200,000 A ...
, the Oort constants, Oort Limit, an
impact crater An impact crater is a depression (geology), depression in the surface of a solid astronomical body formed by the hypervelocity impact event, impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal c ...
on
Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of Trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Su ...
( Oort), and the asteroid 1691 Oort were all named after him.


Early life and education

Oort was born in Franeker, a small town in the Dutch province of
Friesland Friesland ( ; ; official ), historically and traditionally known as Frisia (), named after the Frisians, is a Provinces of the Netherlands, province of the Netherlands located in the country's northern part. It is situated west of Groningen (p ...
, on April 28, 1900. He was the second son of Abraham Hermanus Oort, a physician, who died on May 12, 1941, and Ruth Hannah Faber, who was the daughter of Jan Faber and Henrietta Sophia Susanna Schaaii, and who died on November 20, 1957. Both of his parents came from families of clergymen, with his paternal grandfather, a Protestant clergyman with liberal ideas, who "was one of the founders of the more liberal Church in Holland" and who "was one of the three people who made a new translation of the Bible into Dutch." The reference is to Henricus Oort (1836–1927), who was the grandson of a famous
Rotterdam Rotterdam ( , ; ; ) is the second-largest List of cities in the Netherlands by province, city in the Netherlands after the national capital of Amsterdam. It is in the Provinces of the Netherlands, province of South Holland, part of the North S ...
preacher and, through his mother, Dina Maria Blom, the grandson of theologian Abraham Hermanus Blom, a "pioneer of modern biblical research". Several of Oort's uncles were pastors, as was his maternal grandfather. "My mother kept up her interests in that, at least in the early years of her marriage", he recalled. "But my father was less interested in Church matters." In 1903 Oort's parents moved to
Oegstgeest Oegstgeest () is a town and municipality in the province of South Holland in the western Netherlands. Its population was in . Etymology The portion ''geest'' in the name refers to the Geest, geest lands, which were excavated in the seventeent ...
, near
Leiden Leiden ( ; ; in English language, English and Archaism, archaic Dutch language, Dutch also Leyden) is a List of cities in the Netherlands by province, city and List of municipalities of the Netherlands, municipality in the Provinces of the Nethe ...
, where his father took charge of the Endegeest Psychiatric Clinic. Oort's father, "was a medical director in a sanitorium for nervous illnesses. We lived in the director's house of the sanitorium, in a small forest which was very nice for the children, of course, to grow up in." Oort's younger brother, John, became a professor of plant diseases at the University of Wageningen. In addition to John, Oort had two younger sisters and an elder brother who died of diabetes when he was a student. Oort attended primary school in Oegstgeest and secondary school in Leiden, and in 1917 went to Groningen University to study physics. He later said that he had become interested in science and astronomy during his high-school years, and conjectured that his interest was stimulated by reading
Jules Verne Jules Gabriel Verne (;''Longman Pronunciation Dictionary''. ; 8 February 1828 – 24 March 1905) was a French novelist, poet and playwright. His collaboration with the publisher Pierre-Jules Hetzel led to the creation of the ''Voyages extraor ...
. His one hesitation about studying pure science was the concern that it "might alienate one a bit from people in general", as a result of which "one might not develop the human factor sufficiently." But he overcame this concern and ended up discovering that his later academic positions, which involved considerable administrative responsibilities, afforded a good deal of opportunity for social contact. Oort chose Groningen partly because a well known astronomer, Jacobus Cornelius Kapteyn, was teaching there, although Oort was unsure whether he wanted to specialize in physics or astronomy. After studying with Kapteyn, Oort decided on astronomy. "It was the personality of Professor Kapteyn which decided me entirely", he later recalled. "He was quite an inspiring teacher and especially his elementary astronomy lectures were fascinating." Oort began working on research with Kapteyn early in his third year. According to Oort one professor at Groningen who had considerable influence on his education was physicist Frits Zernike. After taking his final exam in 1921, Oort was appointed assistant at Groningen, but in September 1922, he went to the
United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
to do graduate work at
Yale Yale University is a private Ivy League research university in New Haven, Connecticut, United States. Founded in 1701, Yale is the third-oldest institution of higher education in the United States, and one of the nine colonial colleges ch ...
and to serve as an assistant to Frank Schlesinger of the Yale Observatory.


Career

At Yale, Oort was responsible for making observations with the Observatory's
zenith telescope A zenith telescope is a type of telescope that is designed to point straight up at or near the zenith. They are used for precision measurement of star positions, to simplify telescope construction, or both. A classic zenith telescope, also known ...
. "I worked on the problem of latitude variation", he later recalled, "which is quite far away from the subjects I had so far been studying." He later considered his experience at Yale useful as he became interested in "problems of fundamental astronomy that efelt was capitalized on later, and which certainly influenced isfuture lectures in Leiden." Personally, he "felt somewhat lonesome in Yale", but also said that "some of my very best friends were made in these years in New Haven."


Early discoveries

In 1924, Oort returned to the Netherlands to work at
Leiden University Leiden University (abbreviated as ''LEI''; ) is a Public university, public research university in Leiden, Netherlands. Established in 1575 by William the Silent, William, Prince of Orange as a Protestantism, Protestant institution, it holds the d ...
, where he served as a research assistant, becoming Conservator in 1926, Lecturer in 1930, and Professor Extraordinary in 1935. In 1926, he received his doctorate from Groningen with a thesis on the properties of high-velocity stars. The next year, Swedish astronomer Bertil Lindblad proposed that the rate of rotation of stars in the outer part of the galaxy decreased with distance from the galactic core, and Oort, who later said that he believed it was his colleague Willem de Sitter who had first drawn his attention to Lindblad's work, realized that Lindblad was correct and that the truth of his proposition could be demonstrated observationally. Oort provided two formulae that described galactic rotation; the two constants that figured in these formulae are now known as "Oort's constants". Oort "argued that just as the outer planets appear to us to be overtaken and passed by the less distant ones in the solar system, so too with the stars if the Galaxy really rotated", according to the ''Oxford Dictionary of Scientists''. He "was finally able to calculate, on the basis of the various stellar motions, that the Sun was some 30,000 light-years from the center of the Galaxy and took about 225 million years to complete its orbit. He also showed that stars lying in the outer regions of the galactic disk rotated more slowly than those nearer the center. The Galaxy does not therefore rotate as a uniform whole but exhibits what is known as 'differential rotation'." These early discoveries by Oort about the Milky Way overthrew the Kapteyn system, named after his mentor, which had envisioned a galaxy that was symmetrical around the Sun. As Oort later noted, "Kapteyn and his co-workers had not realized that the absorption in the galactic plane was as bad as it turned out to be." Until Oort began his work, he later recalled, "the Leiden Observatory had been concentrating entirely on positional astronomy, meridian circle work and some proper motion work. But no astrophysics or anything that looked like that. No structure of the galaxy, no dynamics of the galaxy. There was no one else in Leiden who was interested in these problems in which I was principally interested, so the first years I worked more or less by myself in these projects. De Sitter was interested, but his main line of research was celestial mechanics; at that time the expanding universe had moved away from his direct interest." As the European Space Agency states, Oort "sh okthe scientific world by demonstrating that the Milky Way rotates like a giant ' Catherine Wheel'." He showed that all the stars in the galaxy were "travelling independently through space, with those nearer the center rotating much faster than those further away." This breakthrough made Oort famous in the world of astronomy. In the early 1930s he received job offers from
Harvard Harvard University is a private Ivy League research university in Cambridge, Massachusetts, United States. Founded in 1636 and named for its first benefactor, the Puritan clergyman John Harvard, it is the oldest institution of higher lear ...
and
Columbia University Columbia University in the City of New York, commonly referred to as Columbia University, is a Private university, private Ivy League research university in New York City. Established in 1754 as King's College on the grounds of Trinity Churc ...
, but chose to stay at Leiden, although he did spend half of 1932 at the Perkins Observatory, in
Delaware Delaware ( ) is a U.S. state, state in the Mid-Atlantic (United States), Mid-Atlantic and South Atlantic states, South Atlantic regions of the United States. It borders Maryland to its south and west, Pennsylvania to its north, New Jersey ...
,
Ohio Ohio ( ) is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Lake Erie to the north, Pennsylvania to the east, West Virginia to the southeast, Kentucky to the southwest, Indiana to the ...
. In 1934, Oort became assistant to the director of Leiden Observatory; the next year he became General Secretary of the
International Astronomical Union The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...
(IAU), a post he held until 1948; in 1937 he was elected to the
Royal Academy The Royal Academy of Arts (RA) is an art institution based in Burlington House in Piccadilly London, England. Founded in 1768, it has a unique position as an independent, privately funded institution led by eminent artists and architects. Its ...
. In 1939, he spent half a year in the U.S., and became interested in the
Crab Nebula The Crab Nebula (catalogue designations M1, NGC 1952, Taurus A) is a supernova remnant and pulsar wind nebula in the constellation of Taurus (constellation), Taurus. The common name comes from a drawing that somewhat resembled a crab with arm ...
, concluding in a paper, written with American astronomer Nicholas Mayall, that it was the result of a
supernova A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...
explosion.


Nazi invasion of Netherlands

In 1940,
Nazi Germany Nazi Germany, officially known as the German Reich and later the Greater German Reich, was the German Reich, German state between 1933 and 1945, when Adolf Hitler and the Nazi Party controlled the country, transforming it into a Totalit ...
invaded the Netherlands. Soon after, the occupying regime dismissed all Jewish professors from
Leiden University Leiden University (abbreviated as ''LEI''; ) is a Public university, public research university in Leiden, Netherlands. Established in 1575 by William the Silent, William, Prince of Orange as a Protestantism, Protestant institution, it holds the d ...
and other universities. "Among the professors who were dismissed", Oort later recalled, "was a very famous … professor of law by the name of Meyers. On the day when he got the letter from the authorities that he could no longer teach his classes, the dean of the faculty of law went into his class … and delivered a speech in which he started by saying, 'I won't talk about his dismissal and I shall leave the people who did this, below us, but will concentrate on the greatness of the man dismissed by our aggressors.'" This speech (26 November 1940) made such an impression on all his students that on leaving the auditorium they defiantly sang the anthem of the Netherlands and went on strike. Oort was present for the lecture and was greatly impressed. This occasion formed the beginning of the active resistance in Holland. The speech by Rudolph Cleveringa, the dean of the faculty of Law and former graduate student of professor Meijers, was widely circulated during the rest of the war by the resistance groups. Oort was in a little group of professors in Leiden who came together regularly and discussed the problems the university faced in view of the German occupation. Most of the members of this group were put in hostage camps soon after the speech by Cleveringa. Oort refused to collaborate with the occupiers, "and so we went down to live in the
country A country is a distinct part of the world, such as a state, nation, or other political entity. When referring to a specific polity, the term "country" may refer to a sovereign state, state with limited recognition, constituent country, ...
for the rest of the war." Resigning from the Royal Academy, from his professorial post at Leiden, and from his position at the Observatory, Oort took his family to Hulshorst, a quiet village in the province of
Gelderland Gelderland ( , ), also known as Guelders ( ) in English, is a Provinces of the Netherlands, province of the Netherlands, located in the centre-east of the country. With a total area of of which is water, it is the largest province of the Nethe ...
, where they sat out the war. In Hulshorst, he began writing a book on stellar dynamics.


Oort's radio astronomy

Before the war was over, he initiated, in collaboration with a
Utrecht University Utrecht University (UU; , formerly ''Rijksuniversiteit Utrecht'') is a public university, public research university in Utrecht, Netherlands. Established , it is one of the oldest universities in the Netherlands. In 2023, it had an enrollment of ...
student, Hendrik van de Hulst, a project that eventually succeeded, in 1951, in detecting the 21-centimeter radio emission from interstellar hydrogen spectral line at radio frequencies. Oort and his colleagues also made the first investigation of the central region of the Galaxy, and discovered that "the 21-centimeter radio emission passed un-absorbed through the gas clouds that had hidden the center from optical observation. They found a huge concentration of mass there, later identified as mainly stars, and also discovered that much of the gas in the region was moving rapidly outward away from the center." In June 1945, after the end of the war, Oort returned to Leiden, took over as director of the Observatory, and became Full Professor of Astronomy. During this immediate postwar period, he led the Dutch group that built radio telescopes at Radio Kootwijk, Dwingeloo, and Westerbork and used the 21-centimeter line to map the Milky Way, including the large-scale spiral structure, the
Galactic Center The Galactic Center is the barycenter of the Milky Way and a corresponding point on the rotational axis of the galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a ...
, and gas cloud motions. Oort was helped in this project by the Dutch telecommunications company, PTT, which, he later explained, "had under their care all the radar equipment that was left behind by the Germans on the coast of Holland. This radar equipment consisted in part of reflecting telescopes of 7 1/2 meter aperture.... Our radio astronomy was really started with the aid of one of these instruments… it was in Kootwijk that the first map of the Galaxy was made." For a brief period, before the completion of the Jodrell Bank telescope, the Dwingeloo instrument was the largest of its kind on Earth. It has been written that "Oort was probably the first astronomer to realize the importance" of radio astronomy. "In the days before radio telescopes," one source notes, "Oort was one of the few scientists to realise the potential significance of using radio waves to search the heavens. His theoretical research suggested that vast clouds of hydrogen lingered in the spiral arms of the Galaxy. These molecular clouds, he predicted, were the birthplaces of stars." These predictions were confirmed by measurements made at the new radio observatories at Dwingeloo and Westerbork. Oort later said that "it was Grote Reber's work which first impressed me and convinced me of the unique importance of radio observations for surveying the galaxy." Just before the war, Reber had published a study of galactic radio emissions. Oort later commented, "The work of Grote Reber made it quite clear adio astronomywould be a very important tool for investigating the Galaxy, just because it could investigate the whole disc of the galactic system unimpeded by absorption." Oort's work in radio astronomy is credited by colleagues with putting the Netherlands in the forefront of postwar astronomy. Oort also investigated the source of the light from the Crab Nebula, finding that it was polarized, and probably produced by synchrotron radiation, confirming a hypothesis by Iosif Shklovsky.


Comet studies

Oort went on to study comets, which he formulated a number of revolutionary hypotheses. He hypothesized that the Solar System is surrounded by a massive cloud consisting of billions of comets, many of them "long-period" comets that originate in a cloud far beyond the orbits of
Neptune Neptune is the eighth and farthest known planet from the Sun. It is the List of Solar System objects by size, fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 t ...
and
Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of Trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Su ...
. This cloud is now known as the Oort Cloud. He also realized that these external comets, from beyond Pluto, can "become trapped into tighter orbits by
Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...
, and become periodic comets, like
Halley's comet Halley's Comet is the only known List of periodic comets, short-period comet that is consistently visible to the naked eye from Earth, appearing every 72–80 years, though with the majority of recorded apparitions (25 of 30) occurring after ...
." According to one source, "Oort was one of the few people to have seen Comet Halley on two separate apparitions. At the age of 10, he was with his father on the shore at Noordwijk, Netherlands, when he first saw the comet. In 1986, 76 years later, he went up in a plane and was able to see the famous comet once more." In 1951 Oort and his wife spent several months in Princeton and Pasadena, an interlude that led to a paper by Oort and Lyman Spitzer on the acceleration of interstellar clouds by O-type stars. He went on to study high-velocity clouds. Oort served as director of the Leiden Observatory until 1970. After his retirement, he wrote comprehensive articles on the galactic center and on superclusters and published several papers on the quasar absorption lines, supporting Yakov Zel'dovich's pancake model of the universe. He also continued researching the Milky Way and other galaxies and their distribution until shortly before his death at 92. One of Oort's strengths, according to one source, was his ability to "translate abstruse mathematical papers into physical terms," as exemplified by his translation of the difficult mathematical terms of Lindblad's theory of differential galactic rotation into a physical model. Similarly, he "derived the existence of the comet cloud on the outskirts of the Solar System from the observations, using the mathematics needed in dynamics, but then deduced the origin of this cloud using general physical arguments and a minimum of mathematics."


Personal life

In 1927, Oort married Johanna Maria (Mieke) Graadt van Roggen (1906–1993). They had met at a university celebration at Utrecht, where Oort's brother was studying biology at the time. Oort and his wife had two sons, Coenraad (Coen) and
Abraham Abraham (originally Abram) is the common Hebrews, Hebrew Patriarchs (Bible), patriarch of the Abrahamic religions, including Judaism, Christianity, and Islam. In Judaism, he is the founding father who began the Covenant (biblical), covenanta ...
, and a daughter, Marijke. Abraham became a professor of climatology at
Princeton University Princeton University is a private university, private Ivy League research university in Princeton, New Jersey, United States. Founded in 1746 in Elizabeth, New Jersey, Elizabeth as the College of New Jersey, Princeton is the List of Colonial ...
. According to the website of Leiden University, Oort was very interested in and knowledgeable about art. " en visiting another country he would always try to take some time off to visit the local museums and exhibitions…and in the fifties served for some years as chairman of the pictorial arts committee of the Leiden Academical Arts Centre, which had among other things the task of organizing expositions". "Colleagues remembered him as a tall, lean and courtly man with a genial manner," reported his ''New York Times'' obituary.


Honours

Awards *
Bruce Medal The Catherine Wolfe Bruce Gold Medal is awarded every year by the Astronomical Society of the Pacific for outstanding lifetime contributions to astronomy. It is named after Catherine Wolfe Bruce, an American patroness of astronomy, and was ...
of the Astronomical Society of the Pacific in 1942 *
Gold Medal of the Royal Astronomical Society The Gold Medal of the Royal Astronomical Society is the highest award given by the Royal Astronomical Society (RAS). The RAS Council have "complete freedom as to the grounds on which it is awarded" and it can be awarded for any reason. Past awar ...
in 1946 * Janssen Medal from the
French Academy of Sciences The French Academy of Sciences (, ) is a learned society, founded in 1666 by Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French Scientific method, scientific research. It was at the forefron ...
in 1946 * Prix Jules Janssen, the highest award of the Société astronomique de France, the French astronomical society (1947) *
Henry Norris Russell Lectureship The Henry Norris Russell Lectureship is awarded each year by the American Astronomical Society in recognition of a lifetime of excellence in astronomical research. The idea for the lectureship came from then society President Harlow Shapley in 1945, ...
of the
American Astronomical Society The American Astronomical Society (AAS, sometimes spoken as "double-A-S") is an American society of professional astronomers and other interested individuals, headquartered in Washington, DC. The primary objective of the AAS is to promote the adv ...
in 1951 * Gouden Ganzenveer in 1960 * Vetlesen Prize in 1966 * National Radio Astronomy Observatory, Jansky Prize, 1967 * Karl Schwarzschild Medal of the Astronomische Gesellschaft in 1972 * Association pour le Développement International de l'Observatoire de Nice, ADION medal, 1978 * Balzan Prize for
Astrophysics Astrophysics is a science that employs the methods and principles of physics and chemistry in the study of astronomical objects and phenomena. As one of the founders of the discipline, James Keeler, said, astrophysics "seeks to ascertain the ...
in 1984 * Inamori Foundation, Kyoto Prize, 1987 Named after him * 1691 Oort (asteroid) *
Oort cloud The Oort cloud (pronounced or ), sometimes called the Öpik–Oort cloud, is scientific theory, theorized to be a cloud of billions of Volatile (astrogeology), icy planetesimals surrounding the Sun at distances ranging from 2,000 to 200,000 A ...
( Öpik–Oort cloud) * Oort limit * Oort constants
Oort building
the current building of the Leiden Observatory Memberships * Member of the Royal Netherlands Academy of Arts and Sciences (1937–1943, 1945–) * Member of the
American Academy of Arts and Sciences The American Academy of Arts and Sciences (The Academy) is one of the oldest learned societies in the United States. It was founded in 1780 during the American Revolution by John Adams, John Hancock, James Bowdoin, Andrew Oliver, and other ...
(1946–) * Members of the United States
National Academy of Sciences The National Academy of Sciences (NAS) is a United States nonprofit, NGO, 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 ...
(1953–) * Member of the
American Philosophical Society The American Philosophical Society (APS) is an American scholarly organization and learned society founded in 1743 in Philadelphia that promotes knowledge in the humanities and natural sciences through research, professional meetings, publicat ...
(1957–) Upon his death, Nobel Prize winning astrophysicist Subrahmanyan Chandrasekhar remarked, "The great oak of Astronomy has been felled, and we are lost without its shadow."


References


Notes


Biographical materials

* Blaauw, Adriaan, ''Biographical Encyclopedia of Astronomers'' (Springer, NY, 2007), pp. 853–55. * Chapman, David M.F., "Reflections: Jan Hendrik Oort – Swirling Galaxies and Clouds of Comets," JRASC 94, 53–54 (2000). * ESA Space Science, "Comet Pioneer: Jan Hendrik Oort," 27 February 2004. * Katgert-Merkelijn, J., University of Leiden
"Jan Oort, Astronomer"
* Katgert-Merkelijn, J.K.: ''The letters and papers of Jan Hendrik Oort, as archived in the University Library, Leiden''. Dordrecht, Kluwer Academic Publishers, 1997. . * Oort, J.H., "Some Notes on My Life as an Astronomer," Annual Review of Astronomy & Astrophysics 19, 1 (1981). * van de Hulst, H.C., ''Biographical Memoirs of the Royal Society of London'' 40, 320–26 (1994). * van der Kruit, Pieter C.: ''Jan Hendrik Oort. Master of the Galactic System''. Springer Nature, 2019. . * van Woerden, Hugo, Willem N. Brouw, and Henk C. van de Hulst, eds., "Oort and the Universe: A Sketch of Oort's Research and Person" (D. Reidel, Dordrecht, 1980).


Obituaries

* Blaauw, Adriaan, Zenit jaarg, 196–210 (1993). * Blaauw, Adriaan & Maarten Schmidt, PASP 105, 681 (1993). * Blaauw, Adriaan, "Oort im Memoriam," in Leo Blitz & Peter Teuben, eds., 169th IAU Symposium: Unsolved Problems of the * Milky Way, (Kluwer Acad. Publishers, 1996), pp. xv–xvi. * Pecker, J.-C., "La Vie et l'Oeuvre de Jan Hendrik Oort," Comptes Rendus de l'Acadèmie des Sciences: La Vie des Science 10, 5, 535–40 (1993). * van de Hulst, H.C., QJRAS 35, 237–42 (1994). * van den Bergh, Sidney, "An Astronomical Life: J.H. Oort (1900–1992)," JRASC 87, 73–76 (1993). * Woltjer, L., J. Astrophys. Astron. 14, 3–5 (1993). * Woltjer, Lodewijk, Physics Today 46, 11, 104–05 (1993).


Literature

* * * *


External links


Oral history interview transcript with Jan Oort on 10 November 1977
American Institute of Physics, Niels Bohr Library & Archives *
Jan Oort, astronomer (Leiden University Library, April–May 2000)
Online exhibition {{DEFAULTSORT:Oort, Jan 1900 births 1992 deaths Academic staff of Leiden University Foreign associates of the National Academy of Sciences Foreign members of the Royal Society Foreign members of the Russian Academy of Sciences Foreign members of the USSR Academy of Sciences Kyoto laureates in Basic Sciences Members of the American Philosophical Society Members of the Royal Netherlands Academy of Arts and Sciences People from Franekeradeel Presidents of the International Astronomical Union Recipients of the Gold Medal of the Royal Astronomical Society University of Groningen alumni Vetlesen Prize winners