The Observatoire de Paris is opening its historic domes for free on 20 September
Imagine walking through the same rooms as the astronomers who drew the first maps of the French sky, and doing it for free, right in the heart of Paris. That is exactly what the Observatoire de Paris is offering on Sunday 20 September 2026, as part of the European Heritage Days.
One Sunday to step inside a place founded more than 350 years ago
Founded in 1667, the Observatoire de Paris is one of the oldest observatories in the world still in operation. Its original building, designed by architect Claude Perrault, the man behind the colonnade of the Louvre, is perfectly aligned with the four cardinal points. That architectural detail is no accident: it speaks to the scientific rigour that shaped its construction and continues to guide the research carried out there today.
Because this is no frozen museum. Internationally renowned researchers conduct cutting-edge work in astronomy and astrophysics on these very premises. Visiting the institution means both crossing several centuries of the history of science and brushing up against research that is very much alive.
What visitors will be able to see on 20 September
The guided tour programme, each visit lasting one hour, grants access to spaces that are rarely open to the general public. Several highlights stand out along the route.
- The panoramic terrace, offering a sweeping view over the capital
- The Arago dome and its large astronomical refractor dating from 1854
- The monumental room known as the “Cassini” room, engraved with the Paris meridian
- The Grande Galerie and its collection of historic scientific instruments
- The Council Room, with its painted ceiling and portrait gallery
Visitors will also be able to admire the Arago medallions, the meridian and equatorial telescopes installed in the gardens, and the speaking-clock room. Each space tells a chapter in the story of French institutional astronomy, from the earliest observations to the instruments of the 19th century.
A scientific heritage as much as an architectural one
The appeal of the Observatoire de Paris goes well beyond its classical architecture. The historic telescopes, astronomical clocks and celestial globes preserved on site form an exceptional collection of period instruments. These objects offer a tangible sense of how astronomers worked before the digital age.
The building itself is also listed among the major landmarks of French classicism. Designed by Claude Perrault, it stands as a direct testament to the scientific and architectural ambitions of the 17th century. In that sense, a visit here sits at the crossroads of art history and the history of science.
Practical information and how to book your spot
Visits take place on Sunday 20 September 2026, from 12:00 to 17:00, at 98 boulevard Arago, 75014 Paris. Entry is entirely free, but booking is compulsory. Places can be reserved on the Billetweb platform, via the dedicated page for the 2026 Journées du Patrimoine at the Observatoire de Paris.
Allow one hour for the guided tour when planning your day. Astronomers based at the observatory accompany each group, making this a rare opportunity to speak directly with active scientists at one of France’s leading astrophysics research centres.
