About Ernst Öpik
Ernst Julius Öpik (22 October [O.S. 10 October] 1893 – 10 September 1985) was an Estonian astronomer and astrophysicist who spent the second half of his career (1948–1981) at the Armagh Observatory in Northern Ireland. He is best known for his pioneering work on solar system dynamics, particularly of the Oort cloud and the Yarkovsky effect. == Education == 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. == 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 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. 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.
Biography source: Wikipedia. The profile adds birthday-specific historical context from the Celebs Birthday Today editorial database.