To mark the 100th anniversary of the merger of the Paris and Meudon observatories, the Paris Observatory – PSL organised an original experiment : sending a green laser beam to symbolically link the domes of its two historic sites !
Starting from Meudon, the beam travelled across the sky to the Arago dome in Paris, before returning to its starting point. A round-trip journey of approximately 17 kilometres, covered by the light in just 56.19 microseconds ! This travel time was measured live by the Observatory’s teams.
This experiment echoes a historic discovery made 350 years ago, in 1676, when the astronomer Ole Rømer demonstrated at the Paris Observatory that light travels at a finite speed. An event at the crossroads of history, science and heritage.
