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.

Öpik was born in Kunda, Kreis Wierland, Governorate of Estonia then a part of the Russian Empire.

[5][6] 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.

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.

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 approaching Red Army 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 camps.