Jacobus Kapteyn
Dutch astronomer, best known for his extensive studies of the Milky Way and as the first discoverer of evidence for galactic rotation (1851-1922) · Netherlands · On the map · Scientists · Died at 71
Jacobus Cornelius Kapteyn was a Dutch astronomer. He carried out extensive studies of the Milky Way. He found that the apparent movement of stars was not randomly distributed but had two preferential directions: the two star streams. This discovery was later reinterpreted as evidence for galactic rotation.
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A typical day, 30 days to 6 November 2026
The middle day of the days counted, so one week of news cannot move it. The line under it is the last 104 days, one point a day.
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Kapteyn also suggested that these stellar velocities could be used to find the amount of non-luminous matter in the galaxy, which his student, Jan Oort, measured in 1932, referring to it as "invisible matter".
