Ernst Öpik | |
|---|---|
 Ernst Öpik | |
| Born | (1893-10-22)22 October 1893 Kunda,Governorate of Estonia, Russian Empire |
| Died | 10 September 1985(1985-09-10) (aged 91) Bangor,Northern Ireland, United Kingdom |
| Alma mater | |
| Known for | Öpik–Oort cloud |
| Awards |
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| Scientific career | |
| Fields | Astronomy |
| Institutions | Armagh Observatory |
Ernst Julius Öpik (22 October [O.S. 10 October] 1893 – 10 September 1985) was an Estonianastronomer andastrophysicist who spent the second half of his career (1948–1981) at theArmagh Observatory inNorthern Ireland. He is best known for his pioneering work on solar system dynamics,[1] particularly of theOort cloud and theYarkovsky effect.
Öpik was born inKunda,Kreis Wierland,Governorate of Estonia then a part of theRussian Empire. He went to theUniversity of Moscow to specialize in the study of minor bodies, such asasteroids,comets, andmeteors. He completed his 1923 doctorate at theUniversity of Tartu.
He was the first and longest serving editor of theIrish Astronomical Journal (1950–1980) and frequently published his own research there.[1] In 1916 he published an article there in which he estimated the densities of visual binary stars. Using thewhite dwarf starο2 Eridani B, hedetermined its density as 25,000 times the density of the Sun but concluded that the result is impossible.[2]
In 1922 he published a paper in which he estimated the distance to theAndromeda Galaxy. He determined the distance using a novel astrophysical method based on the observedrotational 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).[3] His method is still widely used.
In 1922 he correctly predicted the frequency ofcraters onMars long before they were detected byspace probes.
In 1932 he postulated a theory concerning the origins of comets in theSolar System. He believed that they originated in a cloud orbiting far beyond the orbit ofPluto. This cloud is now known as theOort 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.[4] He also invented arocking camera for the study of meteors.[5][6] In 1951 he published a paper concerning thetriple-alpha process, describing the burning ofhelium-4 intocarbon-12 in the cores ofred giant stars. However, this achievement is often overlooked becauseEdwin Salpeter's paper on the same subject had already been published by the time Öpik's paper reached Britain and the United States.[7]
TheYarkovsky effect was discovered by the Russian civil engineerIvan 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 his native country in 1944 because the approachingRed Army raised fear among Estonians. Living as a refugee in Germany, he became the Estonianrector of theBaltic University in Exile in thedisplaced persons camps. In 1948 he was offered a post inArmagh and remained there despite offers of lucrative jobs in America. From the early 1960s to the mid-1970s he also held a position at theUniversity 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.
He won theJ. Lawrence Smith Medal from theNational Academy of Sciences in 1960, theMeteoritical Society Frederick C. Leonard Memorial Medal in 1968, the Kepler Gold Medal from theAmerican Association for the Advancement of Science & Meteoritical Society in 1972, theGold Medal of the Royal Astronomical Society in 1975 and theBruce Medal in 1976.
TheOort cloud is sometimes called "Öpik-Oort cloud". TheComet Interceptor's Optical Periscopic Imager for Comets (OPIC) instrument is named after Ernst Öpik to celebrate the first Estonia's contribution to a science mission of theEuropean Space Agency.[9]
Theasteroid2099 Öpik is named in his honour. The craterÖpik on theMartian moonPhobos is also named for him.
He was the father of the atomic physicistUuno Öpik. His grandson,Lembit Öpik, was theLiberal DemocratMember of Parliament forMontgomeryshire inWales from 1997 to 2010.
