Adams, Walter Sydney (1876–1956)

US astronomer. He developed the use of spectroscopy in the study of stars and planets, and found that luminosity and the relative intensities of particular spectral lines could distinguish giant stars from dwarf stars. Spectra could also be used to study the physical properties, motions, and distances of stars.

Adams was born near Antioch, Syria, and studied celestial mechanics at the University of Chicago. His work on stellar spectroscopy began under George Hale at the Yerkes Observatory in Wisconsin. In 1904 he assisted Hale in the establishment of the Mount Wilson Observatory above Pasadena in California, becoming its director 1923.

Adams was involved in a long-term project with other astronomers to determine the absolute magnitudes of stars; together, they found the value for 6,000 stars. A second long-term collaborative project was the determination of the radial velocities of more than 7,000 stars.

In 1925 Adams made an observation of the gravitational field of Sirius B which corroborated Albert Einstein's theory of relativity.

Adams studied the atmosphere of Mars and Venus, reporting in 1932 the presence of carbon dioxide in the atmosphere of Venus and, in 1934, the occurrence of oxygen in concentrations of less than 0.1% on Mars. He was responsible for the design and installation of the 254-cm/100-in and 508-cm/200-in telescopes at Mounts Wilson and Palomar.

At Mount Wilson Adams was able to demonstrate that sunspots have a lower temperature than the rest of the solar disc. He also used Doppler displacements to study the rotation of the Sun.