Born Jan. 19, 1851, in Barneveld; died June 18, 1922, in Amsterdam. Dutch astronomer; specialist in stellar astronomy.
Kapteyn received the doctor of philosophy degree in 1875 from the University of Utrecht.
From 1875 to 1878 he worked at the University of Leiden. He also worked at the University of Groningen, where he became a professor in 1878. From 1896 to 1900, Kapteyn published a survey catalog of 454, 875 stars of the southern sky, compiled on the basis of a large amount of photographic material. In 1906 he worked out a plan for investigating the stellar sky by means of studying 206 selected areas evenly distributed throughout the sky. In 1904 he proposed a theory according to which the motions of the stars with respect to each other (the peculiar motions of stars) are not random but prefer two opposite directions in space (a theory that has not been confirmed). He worked out a number of methods for statistically studying the Milky Way Galaxy.