Paris Observatory

Went today to the Paris Observatory, the world's oldest working obervatory, which is only a 15-minute walk from our apartment. Unfortunately, they wouldn't let me in.

In order to visit, you need to send to the observatory, at least three months in advance, a stamped, self-addressed envelope and and a letter requesting tickets for the tours they give only at 2:30pm on the first Sunday of every month, except holidays. I'm not kidding.

Well, at least I got to see the walls around the grounds. Fun factoids about the Paris Observatory:

• The atomic clock that keeps the official time for the entire world is in the basement.
• The talking clock was invented here.
• The French and the English had a heated debate over whether zero degrees longitude should run through the Paris Observatory or the Greenwich Observatory.
• An astronomer at the observatory, Urbain Jean Leverrier, is credited with discovering Neptune in 1846, by making calculations based on perturbations in the orbit of Uranus. (The actual first sighting, however, was made in Berlin.)
  
  This was hailed as a triumph of French science, but unfortunately the accolades went to poor Leverrier's head -- he insisted, for example, on naming the planet after himself. When news spread that an English astronomer, John Couch Adams, had actually made the correct calculations first, Leverrier tried to discover another planet, this time all by himself.
  
  Based on perturbations in Mercury's orbit, Leverrier hypothesized the existence of the planet Vulcan. Although no one was able to find it, Leverrier stubbornly insisted till his death that Vulcan existed. (It was partly for this stubornness that Leverrier was fired as director of the observatory.)
  
  The mystery of Mercury's orbit was finally solved in 1915 by Albert Einstein. The correct prediction of Mercury's orbit is considered one of the best validations of Einstein's general theory of relativity.