Saint-Sulpice Observatory

Inside the Church of Saint-Sulpice in Paris, France, an unusual "observatory" has tracked the sun for nearly three centuries. Saint-Sulpice Observatory is not a telescope dome but an astronomical gnomon built directly into the building's floor and walls.

About Saint-Sulpice Observatory

The gnomon of Saint-Sulpice is a precision instrument: a thin brass line set into the marble floor of the church, aligned so a beam of sunlight entering through a small aperture crosses it at solar noon. Rather than viewing distant stars through a lens, the instrument tracks the sun's position across the seasons.

History

It was installed in 1727 at the initiative of clockmaker and astronomer Henry Sully, who wanted a reliable way to determine the exact moment of solar noon for setting church clocks. The design uses an 11-metre marble obelisk in the north transept as part of the sunlight-tracking system, letting the church calculate the timing of solstices and equinoxes with notable accuracy for its era.

Location & getting there

Saint-Sulpice Observatory sits in central Paris, France, inside one of the city's largest churches, making it an easy stop alongside other Left Bank landmarks.

Visiting Saint-Sulpice Observatory

The gnomon can be seen during the church's regular opening hours as part of a visit to Saint-Sulpice; check the church's own visiting information before you go, since access can change around services and restoration work.

See your named star from here

A dedicated telescope isn't part of this instrument, but the same principle applies wherever you stand: every star has fixed coordinates in the sky. If you've named a star with us, you can look up its position in our catalogue and find it from any dark spot near Paris.