Jacobus Cornelius Kapteyn, (January 19, 1851 – June 18, 1922) was a Dutch astronomer, best known for his extensive studies of the Milky Way and as the first discoverer of evidence for galactic rotation. January 19 is the 19th day of the year in the Gregorian Calendar. ... 1851 was a common year starting on Wednesday (see link for calendar). ... June 18 is the 169th day of the year in the Gregorian Calendar (170th in leap years), with 196 days remaining. ... 1922 was a common year starting on Sunday (see link for calendar). ... In ancient Greece and other early civilizations, astronomy consisted largely of astrometry, measuring positions of stars and planets in the sky. ... The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Galaxia Kuklos) is the galaxy in which the Earth is found. ...

Kapteyn was born in Barneveld, and went to the University of Utrecht to study mathematics and physics in 1868. In 1875, after having finished his thesis, he worked for three years at the Leiden Observatory, before becoming the first Professor of Astronomy and Theoretical Mechanics at the University of Groningen, where he remained until his retirement in 1921. Barneveld is a town and municipality in the eastern Netherlands, in the province of Gelderland. ... Utrecht University (Universiteit Utrecht in Dutch) is a university in Utrecht, The Netherlands. ... Wikibooks Wikiversity has more about this subject: School of Mathematics Wikiquote has a collection of quotations by or about: Mathematics Look up Mathematics in Wiktionary, the free dictionary Wikimedia Commons has more media related to: Mathematics Bogomolny, Alexander: Interactive Mathematics Miscellany and Puzzles. ... The willingness to question previously held truths and search for new answers resulted in a period of major scientific advancements, now known as the Scientific Revolution. ... 1868 was a leap year starting on Wednesday (see link for calendar). ... 1875 was a common year starting on Friday (see link for calendar). ... It has been suggested that this article or section be merged with Thesis defence. ... The Leiden Observatory (Sterrewacht Leiden) is an optical observatory in the city of Leiden in the Netherlands. ... A professor is a senior teacher, lecturer and researcher, usually in a college or university. ... Mechanics refers to: a craft relating to machinery (from the Latin mechanicus, from the Greek mechanikos, meaning one skilled in machines), or a range of disciplines in science and engineering. ... Front of the main building of the University of Groningen The University of Groningen (Dutch: Rijksuniversiteit Groningen or RuG) is a university in Groningen, Netherlands. ... Retirement is the status of a worker who has stopped working. ... 1921 was a common year starting on Saturday (see link for calendar). ...

Between 1896 and 1900, lacking an observatory, he volunteered to measure photographic plates taken by David Gill, who was conducting a photographic survey of the southern hemisphere stars at the Cape Town Observatory. The results of this collaboration was the publication of Cape Photographic Durchmusterung, a catalog listing positions and magnitudes for 454,875 stars on the Southern Hemisphere. 1896 was a leap year starting on Wednesday (see link for calendar). ... 1900 is a common year starting on Monday. ... Photographic plates were one of the earliest forms of photographic film, in which a light-sensitive emulsion of silver salts was applied to a glass plate. ... Sir David Gill (June 12, 1843 – January 24, 1914) was a Scottish astronomer who spent much of his career in South Africa. ... In astronomy, many stars are referred to simply by catalogue numbers. ... For alternate meanings see star (disambiguation) Hundreds of stars are visible in this image taken by the Hubble Space Telescope of the Sagittarius Star Cloud in the Milky Way Galaxy. ... The Southern Hemisphere is the half of a planets surface (or celestial sphere) that is south of the equator (the word hemisphere literally means half ball). On Earth it contains four continents (part of Africa, Australia, most of South America, and Antarctica) and four oceans (South Atlantic, Indian, Pacific...

In 1897, as part of the above work, he discovered Kapteyn's Star. At the time, it had the highest proper motion of any star known. Today it is in second place, having been dethroned by Barnard's Star. 1897 was a common year starting on Friday (see link for calendar). ... Kapteyns Star (also known as GJ 191, HD 33793 or CD -45 1841) is a class M0 subdwarf discovered by Jacobus Kapteyn in 1897. ... The proper motion of a star is the motion of the position of the star in the sky (the change in direction in which we see it, as opposed to the radial velocity) after eliminating the improper motions of the stars, which affect their measured coordinates but are not real... Barnards star is a star in the constellation Ophiuchus which is notable for having the largest proper motion (10. ...

In 1904, studying the proper motions 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 by Bertil Lindblad and Jan Oort. 1904 is a leap year starting on a Friday (link will take you to calendar). ... The proper motion of a star is the motion of the position of the star in the sky (the change in direction in which we see it, as opposed to the radial velocity) after eliminating the improper motions of the stars, which affect their measured coordinates but are not real... Bertil Lindblad (Örebro November 26, 1895 – Saltsjöbaden [outside Stockholm] June 25, 1965) was a Swedish astronomer. ... Jan Hendrik Oort (April 28, 1900 – November 5, 1992) was an internationally famous Dutch astronomer. ...

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 and proper motion of stars in 206 zones. This enormous project was the first coordinated statistical analysis in astronomy and involved the cooperation of over 40 different observatories. 1906 was a common year starting on Monday (see link for calendar). ... The apparent magnitude (m) of a star, planet or other heavenly body is a measure of its apparent brightness; that is, the amount of light received from the object. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequenly refined in terms of other characteristics. ... Radial velocity is the velocity of an object in the direction of the line of sight. ... The proper motion of a star is the motion of the position of the star in the sky (the change in direction in which we see it, as opposed to the radial velocity) after eliminating the improper motions of the stars, which affect their measured coordinates but are not real...

He was awarded the Kapteyn retired in 1921 at the age of 70, but on the request of his former student and director of Leiden Observatory Willem de Sitter, Kapteyn went back to Leiden to assist in upgrading the observatory to contemporary astronomical standards. 1921 was a common year starting on Saturday (see link for calendar). ... The Leiden Observatory (Sterrewacht Leiden) is an optical observatory in the city of Leiden in the Netherlands. ... Willem de Sitter (May 6, 1872 – November 20, 1934) was a mathematician, physicist and astronomer. ...

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 40,000 light years in size, the sun being relatively close (2,000 light years) to its center. The model was valid at high galactic latitudes but failed in the galactic plane because of the lack of knowledge of interstellar absorption. 1922 was a common year starting on Sunday (see link for calendar). ... This article is about a celestial body. ... A light year, abbreviated ly, is the distance light travels in one year: roughly 9. ... The Sun is the star at the centre of our Solar system. ... Many galaxies, including the Milky Way in which our Sun and Earth are located, are disk-shaped: the majority of their visible mass (excluding possible dark matter) lies very close to a plane. ... The galactic plane is the plane in which the majority of a flattened galaxys mass lies. ... In astronomy, the interstellar medium (or ISM) is the matter and energy content that exists between the stars (or their immediate circumstellar environment) within a galaxy. ...

It was only after Kapteyn's death, in Amsterdam, that Robert Trumpler determined that the amount of stellar extinction 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 its galactic center. Amsterdam Location Country The Netherlands Province North Holland Population 739,295 (1 January 2005) Coordinates 4°89E - 52°37N Website www. ... Robert Julius Trumpler (October 2, 1886 – September 10, 1956) was a Swiss-American astronomer. ... The Galactic Center is the rotational center of the Milky Way galaxy. ...

The astronomy institute of the University of Groningen is named after Kapteyn. Front of the main building of the University of Groningen The University of Groningen (Dutch: Rijksuniversiteit Groningen or RuG) is a university in Groningen, Netherlands. ...

Honors

Awards

• Gold Medal of the Royal Astronomical Society (1902)
• James Craig Watson Medal (1913)
• Bruce Medal (1913)

Named after him The Gold Medal is the highest award of the Royal Astronomical Society. ... 1902 was a common year starting on Wednesday (see link for calendar). ... The James Craig Watson Medal was established by the bequest of James Craig Watson, and is awarded by the US National Academy of Sciences for contributions to astronomy. ... Link title1913 is a common year starting on Wednesday. ... The Catherine Wolfe Bruce gold medal is awarded every year by the Astronomical Society of the Pacific for outstanding lifetime contributions to astronomy. ... Link title1913 is a common year starting on Wednesday. ...

• Kapteyn crater on the Moon
• Asteroid 818 Kapteynia
• Kapteyn's Star