Universiteit Leiden

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Leiden Classics: The Leiden Observatory, the world’s oldest university observatory

Whether finding signals of dark matter or discovering hydrogen in the vicinity of exoplanets, Leiden astronomers are world players in their field, and they are part of a long tradition: Leiden was the first university in the world to have its own observatory.

Wooden observatory on top of the Academy Building

For a long time, the roof of the Academy Building was home to something extraordinary: the oldest university observatory in the world! As early as 1632, astronomers were peering at the universe from this spot, searching for unknown celestial bodies. In the early years, the wooden tower on the roof was rather sparsely equipped, and the quadrant of Snellius, a theodolite (instrument for measuring angles), was placed in the open air. Later, two rotating domes were added on the roof and the astronomers were provided with more instruments.

The Academy Building with wooden observatory (on the left) on top.

New observatory on the Witte Singel

Mid-way through the 19th century, Professor of Astronomy Frederick Kaiser had ambitious plans for Leiden astronomy. He was aware of the fact that serious research required a professional observatory. It is thanks to Kaiser’s efforts that in 1857, the university began to build a new observatory on the Witte Singel. Not everyone was delighted with this development, since the new building came at the expense of a large portion of the Hortus Botanicus. The observatory on the Academy Building remained in use until 1858, and was subsequently dismantled.

The Leiden Observatory at the Witte Singels is positioned exactly on the East-West axis.

Russian example

Kaiser, of course, had his own ideas regarding the design. He wanted architect Henri Camp to imitate the famous, neoclassic Pulkovo Observatory in St. Petersburg. And that is exactly what happened. Just like its Russian model, the Leiden Observatory is positioned exactly on the East-West axis so that a meridian circle could be used, and astronomers could determine the position of celestial bodies with great precision.


The end of the 19th century marked the beginning of a long period of prosperity for Dutch astronomy. This was partially due to Leiden astronomer Willem de Sitter, who became director of the Observatory in 1919. Together with Albert Einstein, who at the time held a Chair by Special Appointment in Leiden, he studied the consequences of the theory of relativity for cosmology. Einstein could often be found in the Observatory and during this period, two new domes were added to the complex.

A. Einstein, A.S. Eddington, P. Ehrenfest, H.A. Lorentz, en W. de Sitter in Leiden (1920).

Oort cloud

Sitter also recruited the young astronomer Jan Hendrik Oort, who was later to become world famous as the pioneer of radio astronomy. Oort discovered the rotation of the Milky Way and the so-called Oort cloud, a family of comets far away from the Sun. After the Second World War, Oort became director of the Observatory. The Leiden astronomers wanted to look further than their own town and they collected funds to build a new radio telescope in Dwingeloo. Together with their fellow researchers they discovered that the centre of the Milky Way was much more active than had previously been thought.


The Leiden astronomers also played an important role in the establishment of the ESO, the European Southern Observatory. This collaboration between European countries, established in 1962, led first to the building of a large-scale optical telescope in Chile, and later to the building of the Very Large Telescope, which in turn became the world’s foremost observatory. To this day, this is where Leiden astronomers carry out their research. Since the 1970s, their home base has been the Jan-Hendrik Oort Building in the Huygens Laboratory on the Wassenaarseweg.

Leiden astrochemist Ewine van Dishoeck interpret data from the new Europea radio telescope ALMA.

Come and have a look around

What about the Leiden Observatory on the Witte Singel? It is now a historic monument and is being used by amateur astronomers. Maybe you would liketo walk in the footsteps of Kaiser or Oort? Every day (except Monday) we offer a free guided tour of the Old Observatory, between 12:00 hrs. and 15:00 hrs. You even get the opportunity to look through one of the telescopes.

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