University of Tartu Old Observatory

The last of them was the Fraunhofer Great Dorpat Refractor, that was the largest refracting telescope at the time and was constructed in 1824.

[2] Since 1813, Friedrich Georg Wilhelm von Struve worked there and in 1820 he became a professor and director of the observatory.

Johann Heinrich von Mädler, who is known as the creator of the first precise map of the Moon, was appointed as a new director in 1840.

Öpik estimated the distance of the Andromeda Galaxy, created a method to count meteorites and postulated a theory concerning the origins of comets in the Solar System (this in now known as Öpik-Oort Cloud in his honor).

After the occupation of Estonia during World War II, Öpik fled abroad and continued his work in Armagh Observatory.