Hermann Carl Vogel
Vogel came to Potsdam in 1879, and from 1882 he was its Director, remaining so until 1907.
In 1871, before coming to Potsdam he had made the first observations of Doppler Shifts at opposite limbs of the Sun, confirming the solar rotation that was strongly inferred by the motion of sunspots
Vogel and Julius Scheiner are usually credited as being the first person to successfully use the Doppler shift to measure the radial velocities of stars - their work in this field caused a sensation in astronomy. Between 1888 and 1892, reliable Doppler Shifts for fifty stars were obtained (previous work had been attempted from 1868 onwards by William Huggins in London and Angelo Secchi in Rome).
In 1883, he published the first catalog of stellar spectra, and in the course of analying stellar spectra he had discovered spectroscopic binaries, being able to calculate properties such as the diameter of the binary system and its individual components, the orbital velocity and total mass of the system.
In 1889 E.C. Picker ing. of Harvard Observatory, had noticed spectral shifts in Mizar (of the Mizar-Alcor system) which could be explained by it being a binary star. A few months later Vogel noticed analogous shifts in Algol, although this time the companion was too faint to record a spectrum