Jacobus Kapteyn

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For the Dutch-Ghanaian minister, see Jacobus Capitein.

Jacobus Cornelius Kapteyn
Jacobus Kapteyn. Painting by Jan Veth (1921).
Born(1851-01-19)19 January 1851
Barneveld
Died18 June 1922(1922-06-18) (aged 71)
Amsterdam
NationalityNetherlands
Alma materUniversity of Utrecht
Known fordiscovery of evidence for galactic rotation
AwardsBruce Medal 1913
Scientific career
FieldsAstronomy
Groningen. Sir David Gill in background. Painting by Jan Veth
.

Prof Jacobus Cornelius Kapteyn

FRSE LLD (19 January 1851 – 18 June 1922) was a Dutch astronomer. He carried out extensive studies of the Milky Way. He found that the apparent movement of stars was not randomly distributed but had two preferential directions: the two star streams. This discovery was later reinterpreted as evidence for galactic rotation. Kapteyn also suggested that these stellar velocities could be used to find the amount of non-luminous matter in the galaxy.[1]

Biography

Kapteyn was born in Barneveld to Gerrit J. and Elisabeth C. (née Koomans) Kapteyn,[2][3] 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. In 1888 he became a member of the Royal Netherlands Academy of Arts and Sciences.[4]

Between 1896 and 1900, lacking an observatory, he volunteered to measure

Cape Photographic Durchmusterung, a catalog listing positions and magnitudes for 454,875 stars in the Southern Hemisphere
.

In 1897, as part of the above work, he discovered Kapteyn's Star. It had the highest proper motion of any star known until the discovery of Barnard's Star in 1916.

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.

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

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 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 of Leiden Observatory Willem de Sitter, Kapteyn went back to Leiden to assist in upgrading the observatory to contemporary astronomical standards.

His life's work, First attempt at a theory of the arrangement and motion of the sidereal system, was published in 1922, and described a lens-shaped

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.

It was only after Kapteyn's death, in

galactic 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 the Isaac Newton Group of Telescopes on La Palma in the Canary Islands named the Jacobus Kapteyn Telescope (JKT) after him.

His daughter Henrietta (1881-1956) married astronomer Ejnar Hertzsprung.

Honours

Wikimedia Commons has media related to Jacobus Cornelius Kapteyn.

Awards

Named after him

References

  1. ^ Kapteyn, Jacobus Cornelius (1922). "First attempt at a theory of the arrangement and motion of the sidereal system". Astrophysical Journal. 55: 302–327. Bibcode:1922ApJ....55..302K. doi:10.1086/142670. In concurrence with his contemporaries, he used to the term "dark matter" to designate this non-lumininous matter, which was thought to be dust and gas. "It is incidentally suggested that when the theory is perfected it may be possible to determine the amount of dark matter from its gravitational effect.
  2. ISBN 978-0-387-31022-0
    . Retrieved 22 August 2012.
  3. ISBN 978-3-319-10876-6
    .
  4. ^ "Jacob Cornelius Kapteyn (1851 - 1922)". Royal Netherlands Academy of Arts and Sciences. Retrieved 22 July 2015.

External links

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