In the large hall on the second floor of the Observatoire de Paris - built between 1667 and 1671 to a design made by the architect Claude Perrault - is one of the marvels of the Observatory, the great meridian line.
The principle underlying this line is simple. It is based on the measurement of the meridian altitude of the Sun. This changes through the course of a year, from one solstice to the next. Using the gnomon (a greek word signifying pointer), actually just a hole in the wall of the Observatoire de Paris, the Sun’s light entered the large hall forming an elliptical image on the floor : the image would be more or less elongated depending on whether the Sun was high (in Summer) or low (in winter).
The Observatoire de Paris meridian
On this site you will discover the innermost secrets of the Salle méridienne of the Observatoire de Paris. The site was developed by the IMCCE, l’institut de mécanique céleste de l’Observatoire de Paris.