Vogel , Hermann Karl

(1842–1907) German astronomer

Born at Leipzig in Germany, Vogel began as an assistant at the observatory there. He later directed a private observatory and finally moved to Potsdam to work in the new astrophysical observatory, of which he became director in 1882. He was one of the earliest astronomers to devote himself almost exclusively to spectroscopy. His first discovery came in 1871 when he showed that the solar rotation could be measured using spectroscopic Doppler effects, obtaining identical results to those achieved using sunspots as markers.

In 1890 he came across some unusual stellar spectra – in particular that of the variable star Algol. He found that some stars seemed to be both advancing and receding, for their spectral lines periodically doubled showing both a red and a blue shift. He correctly interpreted this as indicating a binary system with two stars so close together that they could not be separated optically, with one star advancing and one receding. When one star is eclipsed by its companion just one spectra will be visible, but as the other emerges the spectral line will appear to double only to disappear again in the next eclipse. Such systems are known as eclipsing binaries.