Ernst Öpik

Ernst Öpik studied at Faculty of Physics and Mathematics of Moscow Imperial University and Gustav Adolf Grammar School. The recorded working language is Estonian, Russian and English. The field of work recorded is astronomy, astrophysics and meteor. Employment is recorded with University of Tartu, Baltic University and Armagh Observatory. Distinctions recorded are Gold Medal of the Royal Astronomical Society, Bruce Medal, J. Lawrence Smith Medal and Leonard Medal.

• Name — Ernst Öpik • Born — 22 October 1893 • Birthplace — Kunda, Governorate of Estonia, Russian Empire • Died — 10 September 1985 • Place of death — Bangor, Northern Ireland, United Kingdom • Relatives — Lembit Öpik (grandson) • Known for — Öpik–Oort cloud • Field — Astronomy • Workplaces — Armagh Observatory • Education — * University of Moscow • University of Tartu • Awards — * Gold Medal of the Royal Astronomical Society in 1975 • Bruce Medal in 1976

Öpik was born in Kunda, Kreis Wierland, Governorate of Estonia then a part of the Russian Empire. He went to the University of Moscow to specialize in the study of minor bodies, such as asteroids, comets, and meteors. He completed his 1923 doctorate at the University of Tartu.

He was the first and longest serving editor of the Irish Astronomical Journal (1950–1980) and frequently published his own research there. In 1916 he published an article there in which he estimated the densities of visual binary stars. Using the white dwarf star ο 2 Eridani B, he determined its density as 25,000 times the density of the Sun but concluded that the result is impossible. In 1922 he published a paper in which he estimated the distance to the Andromeda Galaxy. He determined the distance using a novel astrophysical method based on the observed rotational velocities of the galaxy, which depends on the total mass around which stars are rotating, and on the assumption that the luminosity per unit mass was the same as that of our galaxy. He concluded that the distance was 450 kpc. His result was in good accordance with other estimates of these days (100 to 1000 kpc) and were closer to recent estimates (778 kpc) than Hubble's result (275 kpc). His method is still widely used. In 1922 he correctly predicted the frequency of craters on Mars long before they were detected by space probes. In 1932 he postulated a theory concerning the origins of comets in the Solar System. He believed that they originated in a cloud orbiting far beyond the orbit of Pluto. This cloud is now known as the Oort cloud or alternatively the Öpik-Oort Cloud in his honour. From October 1931 to the end of July 1933, Öpik, Harlow Shapley and Samuel L. Boothroyd headed the Arizona meteor expedition, which detected approximately 22,000 meteors. He also invented a rocking camera for the study of meteors. In 1951 he published a paper concerning the triple-alpha process, describing the burning of helium-4 into carbon-12 in the cores of red giant stars. However, this achievement is often overlooked because Edwin Salpeter's paper on the same subject had already been published by the time Öpik's paper reached Britain and the United States.

The Yarkovsky effect was discovered by the Russian civil engineer Ivan Osipovich Yarkovsky (1844–1902), who worked on scientific problems in his spare time. Writing in a pamphlet around the year 1900, Yarkovsky noted that the diurnal heating of a rotating object in space would cause it to experience a force that, while tiny, could lead to large long-term effects in the orbits of small bodies, especially meteoroids and small asteroids. Yarkovsky's work might have been forgotten had it not been for Öpik, who read Yarkovsky's pamphlet sometime around 1909. Decades later, Öpik discussed the possible importance of the Yarkovsky effect for moving meteoroids about the solar system.

Öpik fled Estonia in 1944 ahead of the approaching Red Army, in fear of a second Soviet occupation of the Baltic states. Living as a refugee in Germany, he became the Estonian rector of the Baltic University in Exile in the displaced persons camps. In 1948 he was offered a post in Armagh and remained there despite offers of lucrative jobs in America. From the early 1960s to the mid-1970s he also held a position at the University of Maryland, which he visited annually, typically for one semester. As air travel became more common, his refusal to fly made travel to the U.S. from Armagh systematically more difficult and he eventually ceased the annual ritual.

• 1951: "Collision probability with the planets and the distribution of planetary matter", Proc. R. Irish Acad. Sect. A, vol. 54, p. 165-199 • 1958: "Physics of Meteor Flight in the Atmosphere". • 1976: "Interplanetary encounters: Close-range gravitational interactions", Elsevier Scientific Publishing Co., "Developments in Solar System and Space Science", vol 2 • 1977: "About dogma in science and other recollections of an astronomer". Annual Review of Astronomy and Astrophysics, vol. 15, p. 1

Ernst Öpik was recorded at birth as Ernst Julius Öpik. His recorded languages were Estonian, Russian and English. 2 children are recorded: Uuno Öpik and Helgi Öpik. Other recorded relations include Lembit Öpik.

Ernst Öpik worked in astronomy, astrophysics, meteor, comet and minor planet. He was employed by University of Tartu, Baltic University, Armagh Observatory, University of Maryland and National University of Uzbekistan named after Mirzo Ulugbek. He belonged to Royal Astronomical Society, Estonian Academy of Sciences, American Academy of Arts and Sciences, National Academy of Sciences and Royal Irish Academy.

Ernst Öpik is recorded as astronomer, astrophysicist, composer, scientist and university teacher.