Adams, Walter Sydney 1876-1956
US astronomer

Born in Antioch, Syria, of US parents, he studied at Dartmouth College, Massachusetts, the University of Chicago and the Yerkes Observatory. In 1904 he went with George Hale to help establish the Mount Wilson Observatory, near Pasadena, California, where he became deputy director and then director (1923-46). He was responsible for the design and installation of the 2.54 and 5.08m telescopes at Mount Wilson and Palomar. He developed spectroscopic methods to relate stellar spectra to luminosity and used this to measure the distance to 6,000 stars. He also used spectroscopic methods to measure the temperature, pressure and density of the light-emitting material in sunspots. In 1915 he obtained the first spectrum of the white dwarf star Sirius B, showed that it was hotter than the Sun, contrary to expectations, and that it had a density 40,000 times that of water. In 1925 he measured the gravitational red shift induced in the light leaving the surface of Sirius B, adding yet further support to Albert Einstein's general theory of relativity. Adams's 1934 observations of Mars showed that the atmosphere had less than 0.1 per cent oxygen. In 1941 he discovered spectral lines introduced by interstellar cyanogen molecules, giving an early clue to the existence of the microwave background radiation in the universe.