September 10, 1919–March 9, 1997

BY JESSE L. GREENSTEIN

ROBERT B. LEIGHTON, William L. Valentine professor of physics emeritus at the California Institute of Technology, was a remarkably ingenious physicist and astrophysicist. He found no instrumentation problem too difficult, especially if it might open a new part of the electromagnetic spectrum to observation. If he found an inexpensive solution, he would build the apparatus in his spare time, for use by others and by himself.

Bob Leighton built, improved, and used cloud chambers to identify and measure new products of cosmic ray collisions. He explored the decay modes of mu-mesons and recognized several of the strange” particles when particle physics was at its beginning. His subject matter evolved from physics to astrophysics as he helped astronomy take on its modern shape. Leighton worked in solar astronomy, improving old instruments on Mount Wilson. With them he discovered the five-minute body oscillation of the Sun by superposing two Doppler photographs of the same area taken in rapid succession, one a negative and one a positive of the other. In a similar way he studied the Sun's magnetic fields, using the difference in Zeeman shifts between photographs taken with opposite senses of polarization.