The Pulkovo Astronomical Observatory (), officially named the Central Astronomical Observatory of the Russian Academy of Sciences at Pulkovo, is the principal astronomical observatory of the Russian Academy of Sciences. It is located 19 km south of Saint Petersburg on Pulkovo Heights above sea level. It is part of the UNESCO World Heritage Site Historic Centre of Saint Petersburg and Related Groups of Monuments. It was formerly known as the Imperial Observatory at Pulkowo. Early years The observatory was opened in 1839. Originally, it was a brainchild of the German/Russian astronomer Friedrich Georg Wilhelm von Struve, who would become its first director (in 1861, his son Otto Wilhelm von Struve succeeded him). The architect was Alexander Bryullov. The observatory was equipped with state-of-the-art devices, one of them being the a aperture refractor, one of the largest refractors in the world at that time (see Great Refractor). In 1885, the observatory was equipped with refractor, which was the biggest usable refractor in the world, until the telescope at the Lick Observatory in California a few years later. Both were built by Alvan Clark & Sons in Massachusetts. The principal line of work of the observatory consisted of determination of coordinates of stars and astronomical constants, such as precession, nutation, aberration and refraction, and also discovering and measuring double stars. The observatory's activities have also been connected to the geographical study of the territory of Russia and development of navigation. The star catalogues, containing the most precise positions of 374, and then 558 stars, were made for the years 1845, 1865, 1885, 1905 and 1930. By the 50th anniversary of the Observatory, they had built an astrophysical laboratory with a mechanical workshop and installed the Europe's largest refractor, (30 inch). Astrophysical research really gained momentum with the appointment of Feodor Bredikhin as a director of the Observatory in 1890 and transfer of Aristarkh Belopolsky from the Moscow Observatory, an expert in stellar spectroscopy and solar research. In 1923, they installed a big Littrow spectrograph, and in 1940 – a horizontal solar telescope, manufactured at a Leningrad factory. After having received an astrograph in 1894, the observatory began its work on astrophotography. In 1927, the Observatory received a zone astrograph and with its help the Russian astronomers catalogued the stars of the near-polar areas of the sky. Regular observation of movements of celestial poles began with the construction of the zenith telescope in