Captan

Jacobus Cornelius Kapteyn (January 19, 1851 - June 18, 1922) was a famous Dutch astronomer.

Born in Barnfeld, the Netherlands in 1851, Captan entered Utrecht University in 1868 to study mathematics and physics. He received his doctorate in physics in 1875 and went to work at the Leiden Observatory. In 1878, Captan became professor of astronomy at the University of Groningen in the Netherlands until his retirement in 1921.

Between 1896 and 1900, Captan studied photos taken in South Africa by British scientist David Gill. In 1900, he published the first photographic catalog specifically for the southern sky-the Cape of Good Hope Photographic Catalog (CPD), which published 454,875 stars within a 19-degree range around the southern celestial pole. This catalog is important information for studying the structure of the Milky Way. In 1897, Captan also discovered a dwarf star with a very high motion. This star was named Captan Star, which is the known star with the second highest motion, second only to Barnard's star. In 1904, Captan proposed the two-flow theory of stars, arguing that stars throughout the sky flow in roughly two directions. This theory laid the foundation for Swedish astronomer Lindblad and Dutch astronomer Ault to later establish a theory of the rotation of the Milky Way. In 1906, Captan proposed uniformly and randomly selecting 206 regions in the sky (Captan Constituency), and that observatories around the world would work together to count stars. These work pioneered statistical astronomy, promoted the development of stellar astronomy and galactic dynamics, and played a huge role in promoting people's understanding of the structure of the Milky Way.

From the results of the stellar count, Captan established a model of the island universe, and believed that the Milky Way was lenticular, 55,000 light-years in diameter and 11,000 light-years thick, with the sun located near its center, 2,000 light-years from the galactic center [1] [2]. Without taking into account the effects of interstellar extinction, he obtained only about half the known size of the Milky Way, but nine times larger than the results given by the famous British astronomer William Herschel. People called his model of the universe the "Captan Universe". After his death, Robert Julius Trumpler estimated the size of the Milky Way from interstellar reddening, which is relatively close to the structure of the Milky Way.

In 1922, Captan died in Amsterdam. In his memory, asteroid No. 818 was named Captan, and a crater on the moon was named after him.