Jacobus Kapteyn

Who was Jacobus Kapteyn?

Jacobus Cornelius Kapteyn, was a Dutch astronomer, best known for his extensive studies of the Milky Way and as the first discoverer of evidence for galactic rotation.

Kapteyn was born in Barneveld to Gerrit J. and Elisabeth C. Kapteyn, 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.

Between 1896 and 1900, lacking an observatory, he volunteered to measure photographic plates taken by David Gill, who was conducting a photographic survey of southern hemisphere stars at the Royal Observatory at the Cape of Good Hope. The results of this collaboration was the publication of 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.