Jacobus Kapteyn
![Jacobus Kapteyn. Painting by [[Jan Veth]] (1921).](https://upload.wikimedia.org/wikipedia/commons/d/dd/Jacobus_Kapteyn.jpg)
Prof
Jacobus Cornelius Kapteyn FRS FRSE LLD (19 January 1851 – 18 June 1922) 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. Kapteyn also suggested that these stellar velocities could be used to find the amount of non-luminous matter in the galaxy.
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