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. Leighton played a key role in 1949 in showing that the mu-meson decay products are two neutrinos and an electron, and he made the first measurement of the energy spectrum of the decay electron (at the time, low statistics experiments suggested that only one neutrino was involved). In 1950 he made the first observation of strange particle decays after the initial discovery of two cases in England in 1947. Over the next seven years, he elucidated many of the properties, e.g., mass, lifetime, decay-modes and energies, of several of the new strange particles, in particular, the lambda, the xi, and what were then called the theta particles (K-mesons). His subject matter evolved from physics to astrophysics as he helped astronomy take on its modern shape. About 1956, Leighton became interested in the physics of the outer layers of the Sun. With characteristic imagination and insight, he devised Doppler shift and Zeeman effect solar cameras. They were applied with striking success to the investigation of magnetic and velocity fields on the sun. With the Zeeman camera, Leighton mapped complicated patterns of the sun's magnetic field with excellent resolution. Even more striking were his discoveries of a remarkable five-minute oscillation in local surface velocities and of a "super-granulation pattern" of horizontal convection currents in large cells of moving material. These solar oscillations have subsequently been recognized as internally trapped acoustic waves, opening up the whole new fields of helioseismology and solar magneto convection. Leighton himself soon realized that solar magneto-convection cells would lead to an effective diffusion of flux on the solar surface (now called Leighton diffusion), and he included it in a dynamo model of the solar cycle. In the early 1960s, Leighton developed and fabricated a novel, inexpensive infrared telescope, which included a simple array of eight lead-sulfide photocells. These cells were surplus from the defense industry; they had been developed for the Sidewinder missile's heat-seeking guidance system. Starting in 1965, he and Gerry Neugebauer used the new telescope to sweep the roughly 70 percent of the sky visible from Mt. Wilson Observatory, collecting the data as squiggles on a strip-chart recorder. This began a new area of infrared astronomy. The resulting Two-Micron Sky