1841-1907

German astronomer who made pioneer spectroscopic studies of stars and refined an earlier star classification system. Working at the Potsdam Astrophysical Observatory, Vogel cataloged more than 4,000 stars and added sub-divisions to Pietro Secchi's classification scheme. He used spectroscopy to measure how fast the sun rotates and how fast some stars are moving away from Earth. He identified two stars as double stars on the basis of their spectra and calculated the sizes of both pairs of stars.