Isadore Epstein (October 23, 1919 in

Tallinn Tallinn is the capital city, capital and List of cities in Estonia, most populous city of Estonia. Situated on a Tallinn Bay, bay in north Estonia, on the shore of the Gulf of Finland of the Baltic Sea, it has a population of (as of 2025) and ...

Estonia Estonia, officially the Republic of Estonia, is a country in Northern Europe. It is bordered to the north by the Gulf of Finland across from Finland, to the west by the Baltic Sea across from Sweden, to the south by Latvia, and to the east by Ru ...

– September 17, 1995 in

New York City New York, often called New York City (NYC), is the most populous city in the United States, located at the southern tip of New York State on one of the world's largest natural harbors. The city comprises five boroughs, each coextensive w ...

) was an

astronomer An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth. Astronomers observe astronomical objects, such as stars, planets, natural satellite, moons, comets and galaxy, galax ...

. Epstein taught

astronomy Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest includ ...

Columbia University Columbia University in the City of New York, commonly referred to as Columbia University, is a Private university, private Ivy League research university in New York City. Established in 1754 as King's College on the grounds of Trinity Churc ...

for 37 years. He completed his Ph.D. at

Princeton University Princeton University is a private university, private Ivy League research university in Princeton, New Jersey, United States. Founded in 1746 in Elizabeth, New Jersey, Elizabeth as the College of New Jersey, Princeton is the List of Colonial ...

, following which he was appointed as an instructor at Columbia in 1950, assistant professor in 1953, associate professor in 1957, and professor in 1971. He was named professor emeritus in 1987. He served as acting departmental chairman in 1959. His early work at Columbia included development of theoretical models of the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

(following on work he did with

Martin Schwarzschild Martin Schwarzschild (May 31, 1912 – April 10, 1997) was a German-American astrophysicist. The Schwarzschild criterion, for the stability of stellar gas against convention, is named after him. Biography Schwarzschild was born in Potsdam ...

at Princeton). He was the first, in this connection, to recognize the importance of the opacity of matter in terms of its resistance to the flow of

solar radiation Sunlight is the portion of the electromagnetic radiation which is emitted by the Sun (i.e. solar radiation) and received by the Earth, in particular the visible light perceptible to the human eye as well as invisible infrared (typically p ...

, leading to the first models of the Sun to give sensible values for its energy output. Epstein was a leader in the first modern surveys to find sites for

observatories An observatory is a location used for observing terrestrial, marine, or celestial events. Astronomy, climatology/meteorology, geophysics, oceanography and volcanology are examples of disciplines for which observatories have been constructed. Th ...

in the Southern Hemisphere. He studied the clarity and stability of the

atmosphere An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

and accessibility of sites in

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

, and

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

during the 1960s. Major observatories were constructed at all the sites he recommended, and he was particularly involved with the establishment of the Leoncito observatory in Argentina. A long term study of stellar motions was instituted there, and Argentina's national observatory was moved to the site. La Silla and Cerro Tololo observatories in Chile were sited based on Epstein's work, and

Mauna Kea Mauna Kea (, ; abbreviation for ''Mauna a Wākea''); is a dormant Shield volcano, shield volcano on the Hawaii (island), island of Hawaii. Its peak is above sea level, making it the List of U.S. states by elevation, highest point in Hawaii a ...

Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...

was sited using his methods of site selection.

Honor

An asteroid discovered at one of the observatories mentioned above, La Silla, named asteroid 2928 Epstein in his honor.

References

{{DEFAULTSORT:Epstein, Isadore Estonian astronomers 1919 births 1995 deaths Scientists from Tallinn Princeton University alumni Columbia University faculty 20th-century American astronomers Estonian emigrants to the United States