- Jacobus Kapteyn
Jacobus Cornelius Kapteyn, (
January 19 ,1851 –June 18 ,1922 ) was a Dutch astronomer, best known for his extensive studies of theMilky Way and as the first discoverer of evidence for galactic rotation.Kapteyn was born in
Barneveld , and went to the University of Utrecht to studymathematics andphysics in 1868. In 1875, after having finished histhesis , he worked for three years at theLeiden Observatory , before becoming the firstProfessor of Astronomy and TheoreticalMechanics at theUniversity of Groningen , where he remained until hisretirement in 1921.Between 1896 and 1900, lacking an observatory, he volunteered to measure
photographic plate s taken byDavid Gill , who was conducting a photographic survey ofsouthern hemisphere stars at theCape Town Observatory . The results of this collaboration was the publication of "Cape Photographic Durchmusterung ", a catalog listing positions and magnitudes for 454,875stars in theSouthern Hemisphere .In 1897, as part of the above work, he discovered
Kapteyn's Star . At the time, it had the highestproper motion of any star known. Today it is in second place, having been dethroned byBarnard's Star .In 1904, studying the
proper motion s of stars, Kapteyn reported that these were not random, as it was believed in that time; stars could be divided into two streams, moving in nearly opposite directions. It was later realized that Kapteyn's data had been the first evidence of the rotation of our Galaxy, which ultimately led to the finding of galactic rotation byBertil Lindblad andJan Oort .In 1906, Kapteyn launched a plan for a major study of the distribution of stars in the Galaxy, using counts of stars in different directions. The plan involved measuring the
apparent magnitude ,spectral type ,radial velocity , andproper motion of stars in 206 zones. This enormous project was the first coordinated statistical analysis in astronomy and involved the cooperation of over forty different observatories.He was awarded the
James Craig Watson Medal in 1913. Kapteyn later retired in 1921 at the age of seventy, but on the request of his former student and director ofLeiden Observatory Willem de Sitter , Kapteyn went back to Leiden to assist in upgrading the observatory to contemporary astronomical standards.His life-work, "First attempt at a theory of the arrangement and motion of the sidereal system" was published in 1922, and described a lens-shaped
island universe of which the density decreased away from the center, now known as the "Kapteyn's Universe " model. In his model the Galaxy was thought to be 40,000light year s in size, thesun being relatively close (2,000 light years) to its center. The model was valid at high galactic latitudes but failed in thegalactic plane because of the lack of knowledge of interstellar absorption.It was only after Kapteyn's death, in
Amsterdam , thatRobert Trumpler determined that the amount ofinterstellar reddening was actually much greater than had been assumed. This discovery increased the estimate of the galaxy's size to 100,000 light years, with the sun replaced to a distance of 30,000 light years from thegalactic center .The astronomy institute of the
University of Groningen is named after Kapteyn. A street in the city of Groningen is also named after Kapteyn: the J.C. Kapteynlaan. And theIsaac Newton Group of Telescopes at the Canary island ofLa Palma named theJacobus Kapteyn Telescope (JKT) after him.Honours
Awards
*Gold Medal of the Royal Astronomical Society (1902)
*James Craig Watson Medal (1913)
*Bruce Medal (1913)Named after him
*Kapteyn crater on theMoon
*Asteroid 818 Kapteynia
*Kapteyn's Star
*Kapteyn Astronomical Institute at the University of Groningen
*Jacobus Kapteyn Telescope (JKT) at La Palma, one of theCanary islands External links
* [http://www.rug.nl/sterrenkunde/onderzoek/geschiedenis?lang=en History of the Kapteyn Institute]
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