Meridian line of St. Sulpice church / Méridienne de l'église St. Sulpice (Paris) - Great Lines of Earth on Waymarking.com

The depicted historic meridian, hidden in the interior of monumental Church of St. Sulpice in Paris centre, is thanks to novel/movie "Da Vinci Code" probably one of the best known meridians worldwide...

The St. Sulpice church hosted its first meridian line in 1727. But the watchmaker Henry de Sully died one year after he started to drawn its meridian line which therefore stayed unfinished, and of which few remainings are still visible (see below the blue arrow). In 1743, the astronomer Charles Le Monnier restarted and finished the project.

The meridian line is drawn on the ground across the church from south to north, up to an obelisk. This line is situated approximately on the Paris meridian, that passes also through the Paris observatory. A hole in a brass plate installed high in the stained glass, projects the image of the sun on the ground. This image crosses the line when it is local noon, at a position depending on the declination of the sun. At the summer solstice, when the sun is the highest in the sky, the disc image of the sun is projected on the southern part of the line. On the contrary, during the winter solstice, the disc image of the sun is projected on the obelisk, on the northern part. Otherwise, the image crosses the line somewhere between these two points.

The meridian line is shown in the Dan Brown's novel "Da Vinci Code", and in the movie made from the book by Ron Howard, where it is described as a mysterious object that hides a well kept secret. However, such meridian lines are quite common in churches, especially in Italy, where they have been created by great astronomers during the 16th and 17th centuries. The knowledge of astronomical instants were important to assess the date of Easter.