University of Tartu Old Observatory

University of Tartu Old Observatory or Tartu Old Observatory (Estonian: Tartu Tähetorn) is an observatory in Tartu, Estonia. Tartu Observatory was an active observatory from 1810 to 1964. The building now serves as a museum and belongs to the University of Tartu Museum.

Construction of the observatory started in 1808. While it was completed in 1810, setting up the necessary instruments took a few years more. The last of them was the Fraunhofer Refractor (Great Dorpat Refractor), that was the largest refracting telescope at the time and was constructed in 1824. It has been titled as "the first modern, achromatic, refracting telescope".

Since 1813, Friedrich Georg Wilhelm von Struve worked there and in 1820 he became a professor and director of the observatory. He studied double stars and was the first to calculate the exact distance to a star. He also created the Struve Geodetic Arc, that is now enlisted as a UNESCO World Heritage Site. Tartu Old Observatory was the first measurement point of that Arc. Struve helped to organize the building of Pulkovo Observatory and when it opened in 1839, he went on to become its director.

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. He popularized astronomy and wrote the book Populäre Astronomie. He was followed by Thomas Clausen and then Peter Carl Ludwig Schwarz.

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