Isadore Epstein (October 23, 1919 in

Tallinn Tallinn () is the most populous and capital city of Estonia. Situated on a bay in north Estonia, on the shore of the Gulf of Finland of the Baltic Sea, Tallinn has a population of 437,811 (as of 2022) and administratively lies in the Harju '' ...

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

– September 17, 1995 in

New York City New York, often called New York City or NYC, is the most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the most densely populated major city in the U ...

) was an

astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either o ...

. Epstein taught

astronomy Astronomy () is a natural science that studies astronomical object, celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and chronology of the Universe, evolution. Objects of interest ...

Columbia University Columbia University (also known as Columbia, and officially as Columbia University in the City of New York) is a private research university in New York City. Established in 1754 as King's College on the grounds of Trinity Church in Manha ...

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

Princeton University Princeton University is a private research university in Princeton, New Jersey. Founded in 1746 in Elizabeth as the College of New Jersey, Princeton is the fourth-oldest institution of higher education in the United States and one of the n ...

, 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 center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared rad ...

(following on work he did with

Martin Schwarzschild Martin Schwarzschild (May 31, 1912 – April 10, 1997) was a German-American astrophysicist. Biography Schwarzschild was born in Potsdam into a distinguished German Jewish academic family. His father was the physicist Karl Schwarzschild and ...

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 Solar irradiance is the power per unit area ( surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Solar irradiance is measured in watts per square metre ...

, 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, geophysical, oceanography and volcanology are examples of disciplines for which observatories have been constructed. Hi ...

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

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. ...

and accessibility of sites in Australia,

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring count ...

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the eas ...

, and

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, t ...

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 In astronomy, stellar kinematics is the observational study or measurement of the kinematics or motions of stars through space. Stellar kinematics encompasses the measurement of stellar velocities in the Milky Way and its satellites as well as ...

was instituted there, and Argentina's national observatory was moved to the site.

La Silla La Silla may refer to: * La Silla Observatory, an astronomical observatory in Chile * Cerro de la Silla, a mountain and natural monument located within the metropolitan area of the city of Monterrey, Nuevo León, in northeastern Mexico. * La S ...

and

Cerro Tololo The Cerro Tololo Inter-American Observatory (CTIO) is an astronomical observatory located on Cerro Tololo in the Coquimbo Region of northern Chile, with additional facilities located on Cerro Pachón about to the southeast. It is approximately ...

observatories in Chile were sited based on Epstein's work, and

Mauna Kea Mauna Kea ( or ; ; abbreviation for ''Mauna a Wākea''); is a dormant volcano on the island of Hawaii. Its peak is above sea level, making it the highest point in the state of Hawaii and second-highest peak of an island on Earth. The peak i ...

Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only ...

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 9 (nine) is the natural number following and preceding . Evolution of the Arabic digit In the beginning, various Indians wrote a digit 9 similar in shape to the modern closing question mark without the bottom dot. The Kshatrapa, Andhra and ...

in his honor.

References

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