Estonia; city of Tartu (German: former Dorpat; also D鰎pt): Astronomical Observatory of Tartu University; built in starting 19th century and UNESCO World heritage sight. Astronomer Wilhelm von Struve (1793-1864) was director of the observatory; from 1820 to 1839. In 1827; he brought the world biggest Fraunhofer refractor to the observatory; published a catalogue of double stars (twin stars) and measured the meridian bow of the baltic states. From 1816 to 1852; von Struve meaasusred the Russian-Scandinavian Struve Geodetic Arc (German: Struve-Bogen) with center here in Tartu observatory; which became UNESCO World heritage sight; in 2005. There is a concrete memorial sculpture; at the observatory.