Jacobus Kapteyn Biography

Jacobus Cornelius Kapteyn was born in Barneveld, Netherlands on January 19, 1851. He attended the University of Utretcht to study mathematics and physics in 1868. After finishing his thesis, he worked in the Leiden Observatory for three years, before becoming the first Professor of Astronomy and Theoretical Mechanics at the University of Groningen. He volunteered to measure photographic plates taken by David Gill , who was constructing a photographic survey of the southern hemisphere stars at the Royal Observatory at the Cape of Good Hope. The collaboration publication, Cape Photographic Durchmusterung, catalogued 454, 875 stars - including values for density, functions of distance, brightness, and spectral class. He devised a sampling system in which the thourough counting of stars in small, selected areas gave indication to the Milky Way's structure. During his observations, he discovered the phenomenon known as stellar streaming; stating that peculiar motions of stars are not randomized, but rather grouped around two opposite, preffered directions in space. Later consideration revealed Kapteyn's data had been the first evidence of rotation in our galaxy, leading to the final conclusion of galactic rotation. In 1906, he launched a major study of the Galaxy's distribution of stars, involving the measurement of apparent magnitude, spectral type, radial velocity, and proper motion of stars in 206 zones - this being the first coordinated statistical analysis in astronomy.

In 1897, his collaboration brought the discovery of Kapteyn's Star - having the highest proper motion of any star until the discovery of Barnard's Star in 1916. He retired from Leiden Observatory in 1921 at the age of seventy. His life work, First Attempt at Theory of the Arrangement and Motion of the Sidereal System, was published in 1922. He discovered a lens-shaped island universe, today known as the Kapteyn Universe. Jacobus Kapteyn has a moon crater, a star, and a telescope named after him for his accomplishments. He was awarded the Gold Medal of the Royal Astronomical Society in 1902, the James Craig Watson Medal in 1913, and a Bruce Medal in 1913.