Adriaan Jan Wesselink (1909–1995) was a Dutch astronomer who worked successively in the Netherlands, South Africa and the United States.
[1] Wesselink was awarded a PhD in 1938 for research into the eclipsing variable star SZ Camelopardalis that used measurements of its brightness from 12000 photographic plates.
[1][2] He remained at Leiden University during the Nazi occupation in the Second World War, maintaining the functioning of the institution following the resignation of many senior staff members.
The Leiden station was located in the grounds of the Union Observatory, Johannesburg, to provide access to the southern skies invisible from Europe.
A new spectrograph was commissioned in 1951 and Wesselink set to work studying the radial velocities of hot, luminous stars in the Milky Way to improve knowledge about the rotation of the disk of the Galaxy.
In collaboration with A. D. Thackeray, he discovered RR Lyrae variable stars in the Magellanic Clouds, which provided much improved measurements of the distances to these two nearby galaxies.