Walter Sydney Adams (December 20, 1876 – May 11, 1956) was an American astronomer.^{[1][2][3][4][5][6]} He is renowned for his pioneering work in spectroscopy.^[7]

Adams was born in Antioch, Ottoman Empire, to Lucien Harper Adams and Nancy Dorrance Francis Adams, missionary parents,^[8] and was brought to the U.S. in 1885^[1] He graduated from Dartmouth College in 1898, then continued his education in Chicago and in Germany. After returning to the U.S., he began a career in Astronomy that culminated when he became director of the Mount Wilson Observatory.

His primary interest was the study of stellar spectra. He worked on solar spectroscopy and co-discovered a relationship between the relative intensities of certain spectral lines and the absolute magnitude of a star. He was able to demonstrate that spectra could be used to determine whether a star was a giant or a dwarf. In 1915 he began a study of the companion of Sirius and found that despite a size only slightly larger than the Earth, the surface of the star was brighter per unit area than the Sun and it was about as massive.^[9] Such a star later came to be known as a white dwarf. In 1925, he reported a gravitational redshift caused by Sirius B; this was regarded as significant confirmation of Albert Einstein's theory of General Relativity. It is now known that his reported measurements were incorrect. Along with Theodore Dunham, he discovered the strong presence of carbon dioxide in the infrared spectrum of Venus.

Adams died at the age of 79 in Pasadena, California.

Awards and honors

• Member of the American Philosophical Society (1915)^[10]
• Gold Medal of the Royal Astronomical Society (1917)^[11]
• Member of the United States National Academy of Sciences (1917)^[12]
• Henry Draper Medal from the National Academy of Sciences (1918)^[13]
• Fellow of the American Academy of Arts and Sciences (1922)^[14]
• Valz Prize from the French Academy of Sciences (1923)^[15]
• Prix Jules Janssen, the highest award of the Société astronomique de France, the French astronomical society (1926)
• Bruce Medal (1928)^[16][17]
• Janssen Medal from the French Academy of Sciences (1934)
• Foreign Member of the Royal Society (ForMemRS) (1950)^[1]
• Henry Norris Russell Lectureship (1947)

Named after him

• The asteroid 3145 Walter Adams.
• The crater Adams, a crater on Mars.^[18]
• The crater Adams on the Moon is jointly named after him, John Couch Adams and Charles Hitchcock Adams.