Jan Oort

thumb|Leiden Observatory centenary, 1961; Left to right: Jan Oort, Hendrick C. van de Hulst. and Pieter Oosterhoff Jan Hendrik Oort (28 April 1900 – 5 November1992) was a Dutch astronomer. Quotes The combined effects of the stars and of Jupiter appear to determine the main statistical features of the orbits of comets. The structure of the cloud of comets surrounding the Solar System and a hypothesis concerning its origin Bulletin of the Astronomical Institutes of the Netherlands 11 408 91–110 3 January 1950 91 https://openaccess.leidenuniv.nl/bitstream/handle/1887/6036/BAN_11_91_110.pdf?sequence=1 From a score of well-observed original orbits it is shown that the "new" long-period comets generally come from regions between about 50000 and 150000 A.U. distance. The sun must be surrounded by a general cloud of comets with a radius of this order, containing about 1011 comets of observable size; the total mass of the cloud is estimated to be of the order of 1/10 to 1/100 of that of the earth. Through the actlllllllllthis cloud into the vicinity of the sun. The structure of the cloud of comets surrounding the Solar System and a hypothesis concerning its origin Bulletin of the Astronomical Institutes of the Netherlands 11 408 91–110 3 January 1950 91 https://openaccess.leidenuniv.nl/bitstream/handle/1887/6036/BAN_11_91_110.pdf?sequence=1 The article indicates how three facts concerning the long-period comets, which hitherto were not well understood, namely the random distribution of orbital planes and of perihelions, and the preponderance of nearly-parabolic orbits, may be considered as necessary consequences of the perturbations acting on the comets. The structure of the cloud of comets surrounding the Solar System and a hypothesis concerning its origin Bulletin of the Astronomical Institutes of the Netherlands 11 408 91–110 3 January 1950 91 https://openaccess.leidenuniv.nl/bitstream/handle/1887/6036/BAN_11_91_110.pdf?sequence=1 (quote from p. 91) The distribution of galaxies is clumpy on all scales, ranging from binaries, triples, and multiples, through groups containing a few and a hundred galaxies, to rich clusters with thousands of members, masses up to 1015±1M☉, and diameters of the order of 10 Mpc. The latter have been discussed by Neta A. Bahcall in a preceding volume of this series. The clusters are at the end of the scale of the more or less regular structures in the Universe. Superclusters Annual Review of Astronomy and Astrophysics 21 1 373–428 1983 10.1146/annurev.aa.21.090183.002105 (quote from p. 373) There exists also another type of galaxy agglomeration. These have diameters between roughly one and ten times those of large clusters, but have much smaller densitities; they are usually irregular, with patchy density variations and no central concentration. The larger and most conspicuous of these agglomerations may contain several clusters, which explains why they have been given the name "superclusters." In their longer dimensions, crossing times exceed the age of the Universe. They are thus unrelaxed. Unrelaxed appearance, together with large size, might be taken as a definition of superclusters. Superclusters Annual Review of Astronomy and Astrophysics 21 1 373–428 1983 10.1146/annurev.aa.21.090183.002105 (quote from p. 373) Quotes about Jan Oort Soon after he joined the Leiden faculty in 1926, Dr. Oort obtained the first direct observational evidence of the Milky Way's rotation. Through complex complex calculations, he measured the relative velocities of stars moving with the rotating galaxy and deduced their distances from the galactic center. In this way, he determined that the Sun and its planets were not even close to the galaxy's center but 30,000 light years away, in the galactic hinterland, traveling an orbit of that center that takes 300 million years to complete. Wilford, John Noble Jan H. Oort, Dutch Astronomer in Forefront of Field, Dies at 92 12 November 1992 The New York Times http://www.nytimes.com/1992/11/12/us/jan-h-oort-dutch-astronomer-in-forefront-of-field-dies-at-92.html External links Category:Astronomers from the Netherlands Category:1900 births Category:1992 deaths