OSA Honorary Member Arnold Sommerfeld was born 5 December 1868 in Konigsberg, Prussia. His parents encouraged Sommerfeld’s intellectual curiosity and he did well in his studies.  At the University of Konigsberg he chose to concentrate on mathematics. After brief positions at Gottingen, Clausthal and Aachen, he became a professor of theoretical physics—and the successor to Boltzmann—at the University of Munich.

Sommerfeld’s work in mathematics led to important contributions in partial differential equations in physics and the theory of gyroscopes. He then turned to the study of atomic spectra. In 1915, he suggested that the circular orbits of the Bohr atom should instead be elliptical ones and postulated a new, azimuthal quantum number to specify these ellipses. He introduced an additional magnetic quantum number to explain the Zeeman Effect. He also predicted fine-structure lines, which were confirmed by Paschen in 1916. 

His first detailed book on wave mechanics appeared in 1929. An inspiring teacher, he was said to have trained more Nobel Laureates than any other professor of his time, although he himself was never awarded that prize. After the Nazis came to power in 1933, he vigorously defended his Jewish colleagues and was denounced by the authorities and forced into retirement. He died in Munich in a tragic accident. His lectures on physics and optics, published as books, remain as lucid, valuable texts.

In 1950, he was named an Honorary Member of OSA in recognition of his preeminent service in the advancement of optics.  For his work Sommerfeld won many prizes including the Lorentz Gold Medal, the Planck Medal, and the Oersted Medal. He was elected to the Royal Society of London, the U.S. National Academy of Sciences, the Academies of Berlin, Munich, Vienna, Göttingen, Budapest, Uppsala, and Madrid, as well as the Academia dei Lincei in Rome, and the Indian Academy of Sciences. He received honorary degrees from many universities including Rostock, Aachen, Calcutta, and Athens.

Arnold Sommerfeld died 26 April 1951.