From the Enlightment to AI
In May 2026, the French Académie des sciences and the National Academy of Sciences in United States have jointly celebrated in Paris two-and-half centuries of collaborations in science, in front of a large public audience gathered in the Auditorium of the Institut de France.
Our perpetual Secretary Etienne Ghys realized 21 podcasts at this occasion. I conceived with him Above Mt. Wilson, stars.. recorded under the historical Meudon Great Refractor from the Observatoire de Paris. Mt. Wilson is a modest summit above Los Angeles. Since the beginning of the XXth century, its telescopes led to many cooperations between US and French astronomers. There Albert Michelson made the very first measurement of a star diameter (Betelgeuse), following a much earlier proposal from the French Hippolyte Fizeau. Today on Mt. Wilson, astronomers from both countries, collaborate on the CHARA interferomer, resolving details on stars and exoplanets.
This image of the star Betelgeuse is due to Miguel Montargès (LESIA/Observatoire de Paris-PSL) and collaborators. et ses collaborateurs. Obtained in 2021 with the ESO Very Large Telescope, it shows some details on the star surface, thanks to the interferometric methods of Fizeau/Michelson/Labeyrie.
In 1910, George Ritchey, engineer and builder of the Hooker telescope of 100 inches diameter, meets on Mt. Wilson the famous French optician Henri Chrétien. A consequene of the encounter is the departure to Paris, in 1920, of Ritchey, where their collaboration led to the famous optical scheme ‘Ritchey-Chrétien”, which provides good images on a large field of view. From then, most of the large telescopes built in the world will follow this optical scheme, as recently the James Webb Space Telescope.
The outward motion of galaxies, caused by the expansion of the universe hence discovered, was observed with the Hooker telescope in 1929 by the astronomer Edwin Hubble.
