Ernst Julius Öpik ( – 10 September 1985) was an Estonian

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 ...

and astrophysicist who spent the second half of his career (1948–1981) at the Armagh Observatory in

Northern Ireland Northern Ireland ( ; ) is a Countries of the United Kingdom, part of the United Kingdom in the north-east of the island of Ireland. It has been #Descriptions, variously described as a country, province or region. Northern Ireland shares Repub ...

. He is best known for his pioneering work on solar system dynamics, particularly of the

Oort cloud The Oort cloud (pronounced or ), sometimes called the Öpik–Oort cloud, is scientific theory, theorized to be a cloud of billions of Volatile (astrogeology), icy planetesimals surrounding the Sun at distances ranging from 2,000 to 200,000 A ...

and the Yarkovsky effect.

Education

Öpik was born in Kunda, Kreis Wierland,

Governorate of Estonia The Governorate of Estonia, also known as the Esthonia (Estland) Governorate, was a province (''guberniya'') and one of the Baltic governorates of the Russian Empire. It was located in the northern Estonia with some islands in the West Estoni ...

then a part of the

Russian Empire The Russian Empire was an empire that spanned most of northern Eurasia from its establishment in November 1721 until the proclamation of the Russian Republic in September 1917. At its height in the late 19th century, it covered about , roughl ...

. He went to the

University of Moscow Moscow State University (MSU), officially M. V. Lomonosov Moscow State University,. is a public research university in Moscow, Russia. The university includes 15 research institutes, 43 faculties, more than 300 departments, and six branches. Al ...

to specialize in the study of minor bodies, such as

asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...

comet A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitationally unbound atmosphere or Coma (cometary), coma surrounding ...

s, and

meteor A meteor, known colloquially as a shooting star, is a glowing streak of a small body (usually meteoroid) going through Earth's atmosphere, after being heated to incandescence by collisions with air molecules in the upper atmosphere, creating a ...

s. He completed his 1923 doctorate at the

University of Tartu The University of Tartu (UT; ; ) is a public research university located in the city of Tartu, Estonia. It is the national university of Estonia. It is also the largest and oldest university in the country.

Astronomical work

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 A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...

star ο₂ 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 The Andromeda Galaxy is a barred spiral galaxy and is the nearest major galaxy to the Milky Way. It was originally named the Andromeda Nebula and is cataloged as Messier 31, M31, and NGC 224. Andromeda has a Galaxy#Isophotal diameter, D25 isop ...

. 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

crater A crater is a landform consisting of a hole or depression (geology), depression on a planetary surface, usually caused either by an object hitting the surface, or by geological activity on the planet. A crater has classically been described ...

s on

Mars Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...

long before they were detected by

space probe Uncrewed spacecraft or robotic spacecraft are spacecraft without people on board. Uncrewed spacecraft may have varying levels of autonomy from human input, such as remote control, or remote guidance. They may also be autonomous, in which th ...

s. In 1932 he postulated a theory concerning the origins of comets in the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

. He believed that they originated in a cloud orbiting far beyond the orbit of

Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of Trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Su ...

. This cloud is now known as the

or alternatively the Öpik-Oort Cloud in his honour. From October 1931 to the end of July 1933, Öpik,

Harlow Shapley Harlow Shapley (November 2, 1885 – October 20, 1972) was an American astronomer, who served as head of the Harvard College Observatory from 1921–1952, and political activist during the latter New Deal and Fair Deal. Shapley used Cepheid var ...

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 The triple-alpha process is a set of nuclear fusion reactions by which three helium-4 nuclei (alpha particles) are transformed into carbon. In stars Helium accumulates in the cores of stars as a result of the proton–proton chain reaction a ...

, describing the burning of

helium-4 Helium-4 () is a stable isotope of the element helium. It is by far the more abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on Earth. Its nucleus is identical to an alpha particle, and consi ...

into

carbon-12 Carbon-12 (12C) is the most abundant of the two stable isotopes of carbon ( carbon-13 being the other), amounting to 98.93% of element carbon on Earth; its abundance is due to the triple-alpha process by which it is created in stars. Carbon-1 ...

in the cores of

red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The stellar atmosphere, outer atmosphere is inflated and tenuous, making the radius large and the surface t ...

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.

Yarkovsky effect connection

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.

Exile

Öpik fled his native country in 1944 because the approaching

Red Army The Workers' and Peasants' Red Army, often shortened to the Red Army, was the army and air force of the Russian Soviet Republic and, from 1922, the Soviet Union. The army was established in January 1918 by a decree of the Council of People ...

raised fear among Estonians. Living as a refugee in Germany, he became the Estonian rector of the Baltic University in Exile in the

displaced persons camp A refugee camp is a temporary settlement built to receive refugees and people in refugee-like situations. Refugee camps usually accommodate displaced people who have fled their home country, but camps are also made for internally displace ...

s. In 1948 he was offered a post in

Armagh Armagh ( ; , , " Macha's height") is a city and the county town of County Armagh, in Northern Ireland, as well as a civil parish. It is the ecclesiastical capital of Ireland – the seat of the Archbishops of Armagh, the Primates of All ...

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 The University of Maryland, College Park (University of Maryland, UMD, or simply Maryland) is a public land-grant research university in College Park, Maryland, United States. Founded in 1856, UMD is the flagship institution of the Univ ...

, 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.

Awards

He won the J. Lawrence Smith Medal from the

National Academy of Sciences The National Academy of Sciences (NAS) is a United States nonprofit, NGO, non-governmental organization. NAS is part of the National Academies of Sciences, Engineering, and Medicine, along with the National Academy of Engineering (NAE) and the ...

in 1960, the

Meteoritical Society The Meteoritical Society is a non-profit scholarly organization founded in 1933 to promote research and education in planetary science with emphasis on studies of meteorites and other extraterrestrial materials that further our understanding of th ...

Frederick C. Leonard Memorial Medal in 1968, the Kepler Gold Medal from the

American Association for the Advancement of Science The American Association for the Advancement of Science (AAAS) is a United States–based international nonprofit with the stated mission of promoting cooperation among scientists, defending scientific freedom, encouraging scientific responsib ...

& Meteoritical Society in 1972, the

Gold Medal of the Royal Astronomical Society The Gold Medal of the Royal Astronomical Society is the highest award given by the Royal Astronomical Society (RAS). The RAS Council have "complete freedom as to the grounds on which it is awarded" and it can be awarded for any reason. Past awar ...

in 1975 and the

Bruce Medal The Catherine Wolfe Bruce Gold Medal is awarded every year by the Astronomical Society of the Pacific for outstanding lifetime contributions to astronomy. It is named after Catherine Wolfe Bruce, an American patroness of astronomy, and was ...

in 1976.

Papers

* 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

Books

* 2004:
Physics of Meteor Flight in the Atmosphere
',

Dover Publications Dover Publications, also known as Dover Books, is an American book publisher founded in 1941 by Hayward and Blanche Cirker. It primarily reissues books that are out of print from their original publishers. These are often, but not always, book ...

Legacy

The

is sometimes called "Öpik-Oort cloud". The

Comet Interceptor The ''Comet Interceptor'' is a robotic spacecraft mission led by the European Space Agency (ESA) planned for launch in 2029. The spacecraft will be "parked" at the Lagrangian point, Sun-Earth L2 point and wait for up to three years for a long-p ...

'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 the

European Space Agency The European Space Agency (ESA) is a 23-member International organization, international organization devoted to space exploration. With its headquarters in Paris and a staff of around 2,547 people globally as of 2023, ESA was founded in 1975 ...

. The

2099 Öpik 2099 Öpik, provisional designation , is a dark and eccentric asteroid and Mars-crosser from the inner regions of the asteroid belt, approximately 5.1 kilometers in diameter. The asteroid was discovered on 8 November 1977, by American astronomer ...

is named in his honour. The crater Öpik on the

Martian Mars, the fourth planet from the Sun, has appeared as a setting in works of fiction since at least the mid-1600s. Trends in the planet's portrayal have largely been influenced by advances in planetary science. It became the most popular celes ...

moon Phobos is also named for him. He was the father of the atomic physicist Uuno Öpik. His grandson, Lembit Öpik, was the Liberal Democrat Member of Parliament for

Montgomeryshire Montgomeryshire ( ) was Historic counties of Wales, one of the thirteen counties of Wales that existed from 1536 until their abolishment in 1974. It was named after its county town, Montgomery, Powys, Montgomery, which in turn was named after ...

Wales Wales ( ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by the Irish Sea to the north and west, England to the England–Wales border, east, the Bristol Channel to the south, and the Celtic ...

from 1997 to 2010.

References

External links

Optical Periscopic Imager for Comets (OPIC) Tartu Observatory Space Exploration Group

Evening Standard (London); "Lembit and his Very Cheeky Family"
{{DEFAULTSORT:Opik, Ernst 1893 births 1985 deaths People from Kunda, Estonia People from Kreis Wierland 20th-century astronomers Estonian astrophysicists Estonian astronomers Planetary scientists 20th-century Estonian scientists Astronomers from Northern Ireland Moscow State University alumni University of Tartu alumni Members of the Estonian Academy of Sciences Foreign associates of the National Academy of Sciences White movement people Estonian World War II refugees Recipients of the Gold Medal of the Royal Astronomical Society Estonian emigrants to Northern Ireland People from Armagh (city) Scientists from County Armagh Irish astrophysicists