Paris Observatory

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The Observatoire de Paris (Paris Observatory, /opsɛʁvatwaʁ də paʁi/) is the oldest operating astronomical observatory in existence, having been founded in 1667, over three centuries ago. The first director of the observatory was Gian Domenico Cassini.

This is a picture of the front of the building, taken in the afternoon; you are looking exactly south. Since the building faces exactly north, the front is almost always in the shade.

The southern face of this building (not visible here) defines the latitude of Paris (48° 50’ 11” north of the Equator). The centerline of the building, upon which I was standing when I took this picture, defines the Paris Meridian (2° 20’ 14.025” east of Greenwich, U.K.).

The observatory is no longer used for astronomical observations, since the light pollution of the metropolis surrounding it makes that impossible. However, in the basement, atomic clocks maintain the atomic time standard for the entire world, on behalf of the Bureau International de l’Heure, which is responsible for maintaining this standard. This is also the location of the speaking clock (time service), which you can reach within France by dialing 3699. The basement also has an opening into the catacombs, although I do not believe it is used for anything.

You can visit the observatory on the first Saturday of each month, if you write and request admission to the tour in advance. The waiting list is several months long.

Photographed in the summer of 2000.