Astronomer Isadore Epstein Dead at 76

Photograph: Epstein.

By Bob Nelson

Isadore Epstein, a Columbia astronomer whose site surveys enabled the construction of observatories in the Southern Hemisphere, died on Sept. 17. He was 76 years old.

His death at St. Luke's-Roosevelt Hospital in Manhattan followed a six-week illness, said his wife, Adela. He was professor emeritus of astronomy and had taught at Columbia for 37 years.

His observatory site surveys were of fundamental importance to 20th-century astronomy, said Michael Rich, a research scientist at the Columbia Astrophysics Laboratory. "The current generation of astronomers has been largely trained on telescopes built at the sites that Epstein first surveyed," Rich said. Epstein also developed theoretical models of stars and made fundamental observations of stars that were useful in determining the size and age of the universe.

The youngest of nine children, he was born in 1919 in Tallinn, Estonia, to Abraham Betsalel Epstein and Anna Malko Czyz Epstein and in 1925 came with his family to Cincinnati.

Epstein did his Ph.D. work at Princeton with Martin Schwarzschild, who developed modern models of the interiors of stars.

He was appointed associate at Columbia in 1950, assistant professor in 1953, associate professor in 1957 and professor in 1971. He served as acting departmental chairman in 1959 and was named professor emeritus in 1987. Early work at Columbia included his development of theoretical models of the sun; that is, calculations predicting the temperature and density at every point in the sun that also resulted in an accurate prediction of the sun's total light output and radius. He recognized that one major uncertainty was the opacity of matter - its resistance to the flow of radiation, because of properties of atoms-- in the Sun's interior. By making intelligent adjustments of this quantity, Epstein was able to produce the first models of the sun that gave sensible values for the radius and energy output.

His most important contribution was his participation in the first modern surveys for observatory sites in the Southern Hemisphere. Epstein studied the clarity, stability of the atmosphere, and accessibility of sites in Australia, South Africa, Chile, and Argentina. Following his surveys in the 1960s, major observatories were built in all of these places, using the data he and a few others collected. He was particularly involved with establishment of an observatory site in El Leoncito, Argentina, where a long-term survey of stellar motions, the Yale-Columbia Proper Motion Survey, was initiated. Columbia has since withdrawn from the project, but El Leoncito is now also the site of Argentina's national observatory.

Among the other sites of major observatories he first surveyed are La Silla and Cerro Tololo, Chile; Southerland in South Africa; and Siding Springs in Australia. "Front-line research currently takes place at every one of these sites, and continued access to the site in Chile has one of the highest priorities in American astronomy," Rich said. It is noteworthy, Rich pointed out, that when Epstein began his site surveys, the only major research instrument in the Southern Hemisphere was an aging, barely usable 74-inch telescope at Bloemfontein, South Africa. The techniques developed in the early surveys have been used to identify observatory sites at Mauna Kea in Hawaii and Cerro Morado in Chile.

In addition to his wife, Epstein is survived by a sister, Esther E. Fish, as well as many nieces and nephews.

Columbia University Record -- October 11, 1996 -- Vol. 22, No. 6