A native of New York City, Greenstein grew up in a family that actively encouraged his scientific interests. At the age of eight he received a brass telescope from his grandfather—not an unusual gift for an American child, but Greenstein soon was also experimenting in earnest with his own prism spectroscope, an arc, a rotary spark, a rectifier, and a radio transmitter. With the spectroscope he began his lifelong interest in identifying the composition of materials, a passion that would lead to his becoming a worldwide authority on the evolution and composition of stars.
Greenstein entered the Horace Mann School for Boys at the age of 11, and by 16 was a student at Harvard University. After earning his bachelor's degree in 1929 and his master's in 1930, he decided that it would be prudent, in the depths of the Great Depression, to join the family's real estate and finance business in New York. But by 1934 he was back at Harvard, earning his doctorate in 1937.
Greenstein won a National Research Council Fellowship in 1937, which allowed a certain amount of latitude in his place of employment. With the stipend, he chose to join the University of Chicago's Yerkes Observatory at Williams Bay, Wisconsin, remaining there for the duration of the two-year fellowship. In 1939 he joined the University of Chicago astrophysics faculty, and during the war years did military research in optical design at Yerkes. He also spent time at McDonald Observatory, then jointly operated by the University of Chicago and the University of Texas, before accepting an offer from the California Institute of Technology to organize a new graduate program in optical astronomy in conjunction with the new 200-inch Hale Telescope at Palomar Observatory.
The Caltech astronomy program quickly became the premier academic program of its kind in the world, with Greenstein serving as department head from 1948 to 1972. During the 24-year period, he spent more than 1,000 observing nights at Palomar and other major observatories, and also took up radio astronomy in 1955. He was a staff member at Mount Wilson and Palomar Observatories until 1979, when he retired from the Caltech faculty, and remained active in research for many years afterward. He stopped observing in 1983, but continued research on white dwarfs, M dwarfs, and the molecular composition of stars. Despite many chances to become an administrator, he remained a researcher for his entire life.
Greenstein's research interests largely centered on the physics of astronomical objects. In addition to stellar composition, he also worked on the synthesis of chemical elements in stellar interiors, studied the physical processes of radio-emitting sources, worked with Caltech colleague Maarten Schmidt on the high redshift of quasars in 1963, demonstrated that quasars are quite compact objects, and discovered and studied more than 500 white dwarfs. In later years, he studied the magnetic fields of white dwarfs, established their luminosities, and worked on ultraviolet spectroscopy with data obtained from the IUE satellite.
A common thread of his research endeavors, Greenstein wrote, "was that they were pioneering thrusts, attempts to provide first tests of a variety of physical laws under extreme conditions in the inaccessible but convenient experimental laboratories of the stars."
Greenstein was active in the establishment of the National Radio Astronomy Observatory, served as chair of the board of the Association of University Research in Astronomy, and was a former member of the Harvard Board of Overseers. He also played a pivotal role in organizing various national astronomical facilities, serving as chair of the 1970 decadal review of astronomy for the National Research Council (for which the Greenstein Report was issued), and served on the National Academy of Sciences' committee on science engineering and public policy.
He was elected to the National Academy of Sciences in 1957.
During his 72-year career in astrophysics, Greenstein was named California Scientist of the Year in 1964, was awarded the NASA Distinguished Public Service Medal in 1974, and the Gold Medal of the Royal Astronomical Society in 1975. He was presented the Centennial Medal by Harvard, and was named to the American Academy of Achievement in 1982.
He is survived by two sons, Peter Greenstein of Oakland, California, and George Greenstein of Amherst, Massachusetts. Naomi Kitay Greenstein, his wife of 68 years, whom he met as a 16-year-old Harvard undergraduate, died earlier this year. The Greensteins were often commended for the warmth and hospitality they extended to astronomers throughout the world. Naomi Greenstein also played a role in building the spirit of the astronomy group at Caltech.
Contact: Robert Tindol (626) 395-3631
