Kapteyn, Jacobus Cornelius (1851–1922)

Dutch astronomer. He analysed the structure of the universe by studying the distribution of stars using photographic techniques. To achieve more accurate star counts he introduced the technique of statistical astronomy.

Kapteyn reported 1904 that the proper motions of stars were not random, as had been believed; stars could be divided into two streams, moving in nearly opposite directions. It was later realized that this data was the first evidence of the rotation of our Galaxy.

Kapteyn was born in Barneveld and studied at Utrecht. After working at the observatory at Leiden, he was professor at Groningen 1875–1921, but had no direct access to any observatory or instrument.

In 1885, Kapteyn volunteered to work with David Gill in a photographic survey of the southern skies from the observatory at the Cape of Good Hope, South Africa. The photographs were analysed at Groningen and published as the huge Cape Photographic Durchmusterung 1896–1900. This presented data on the brightness and positions of 454,875 southern stars. The project also resulted in the foundation of the Kapteyn Astronomical Laboratory.

In 1906 he selected 206 specific stellar zones, aiming to ascertain the magnitudes of all the stars within these zones, as well as to collect data on their spectral type, radial velocity, proper motion, and so on. This enormous project was the first coordinated statistical analysis in astronomy and involved the cooperation of over 40 observatories.