A French sojourn

23 Sep 2011

Richard is not the only one who has been travelling this week. I attended a colloquium in Paris looking at steps to getting more of Europe's, and the world's, observatories recognised as World Heritage sites (currently only a few observatories make the list, usually as part of a larger area: the Royal Observatory in Maritime Greenwich, Pulkovo Observatory in the St Petersburg inscription, Edinburgh's old Royal Observatory falls within the Edinburgh Old and New Towns inscription, Jantar Mantar in Jaipur and some ancient archaeological sites). One proposal is to suggest a route or intinerary of observatories which, collectively, can be considered outstanding world heritage. Such transboundary, multiple-site inscriptions have already been made by UNESCO, for example in the Santiago de Compostela pilgrimage route through France and Spain and, intruigingly, the Struve Geodetic Arc.

The meeting was held at the Institut Astrophysique de Paris, which is right next to the Paris Observatory. I stayed in the IAP for one night, and could see the historic observatory, and the sadly delapidated equatorial building, from my window. The main building dates back to 1667 and the institution, of course, has multiple links with Greenwich and the story of longitude on land and at sea. Perhaps most important were the attempts - by astronomical observations, trigonometical survey and rocket signals - to establish the exact difference in longitude between Greenwich and Paris, so allowing accurate comparisons of data from the two observatories and geodetic surveys by both nations.



Many of the characters we've met in this blog before were involved in these attempts. The 18th-century projects, led by Cassini de Thury, Joseph Banks, William Roy and the Board of Ordnance, can be read about in this article by Jean-Pierre Martin and Anita McConnell. These surveys were remeasured by François Arago and Henry Kater in the 1820s, and John Herschel and Edward Sabine used a chain of observing stations and visual signals (aka rockets) to establish the distance in 1825, on behalf of the Board of Longitude.



Reminders were thick on the ground around the observatory in Paris. The IAP is on Boulevard Arago, where an empty plinth commemorates the astronomer, and the Observatory's entrance is accessed via Avenue de l'Observatoire and Rue Cassini (after Cassini I). Although I forgot to look for it, Paris has also marked the Paris Meridian with the Arago Medallions, exactly 9' 6/10" away from Greenwich's meridian - according to Sabine, Herschel and the Board of Longitude.



Just imagine trying to create a Board of Longitude-themed trail! It would be a long trip.