OUDE STERREWACHT LEIDEN – OBSERVATOIRE DE LEYDE

The University of Leiden, founded in 1575, is the oldest university in the Netherlands! As early as 1633, astronomy began to make its mark with the establishment of an observatory - now the oldest university observatory in the world! - to house a valuable Snellius quadrant (an instrument for measuring distances and angles). For the first two centuries, the observatory was used primarily for educational purposes. In 1861, it was directed by the astronomer Frederik Kaiser who promoted the construction of a new observatory in order to establish astronomy in the Netherlands. At the end of the 19th and the beginning of the 20th century, the city of Leiden became a world-renowned scientific center, with famous physicists such as Paul Ehrenfest, Hendrik Lorentz, Pieter Zeeman and Heike Kamerlingh Onnes, some of whom won Nobel prizes. In 1919, Willem de Sitter became director. A great specialist in the theory of relativity and its implications, he collaborated with Albert Einstein in the early 1930s. From 1945 to 1970, another character took the reins of the site, Jan Hendrik Oort, who a few years later became the most famous Dutch scientist... We owe him in particular the discovery of the famous "Oort cloud", located at the limits of the solar system and well beyond the most distant planets, a true reservoir of comets. From time to time, some of them break away from the cloud to orbit the Sun and become these particular hairy stars that animate our starry skies. During this 20th century, it is clear that the observatories located in cities can no longer remain at the forefront of astronomical research because of the various pollutions caused by human activities, especially lighting. And it is quite natural that following the creation of the European Southern Observatory (ESO) in 1962, Dutch astronomy, as well as that of other European countries, decentralized towards the new observatories built in particular in the southern hemisphere, in Chile. Since the end of the 1970s, astronomers are no longer housed in the observatory building, but in the Jan-Hendrik Oort building and the Huygens laboratory on the Wassenaarseweg. For a while, it looked like the old observatory was going to be abandoned... Fortunately, renovation and rehabilitation works were carried out during the years 2008-2012.