Before you ask, this bizarre word has nothing to do with gnomes! In fact, the term comes from the Greek word gnomon (which means the one who knows) and designates the part of a sundial that casts a shadow.
Actually the one who knows is a pretty good name, as a proper sundial can do much more than just tell the time: it also tells you the exact date and, if you were an ancient astronomer in a previous life, it can help you calculate the exact circumference of the Earth.
One of the most famous gnomons in the world is to be found in the church of Saint-Sulpice, just a ten-minute walk from French Theory. Ever since 2004, the whole world and his dog have been coming to see it, drawn by the many legends that surround the device. Designed to project the image of the sun on the floor, it allows the observer to determine specific moments in the sun’s yearly movement through the skies above (solstice, equinox etc). All you need to do is to look at the image’s position on a north-south meridian – a brass line embedded in the floor of the church
L'obélisque de Saint-Sulpice. Wikimedia Commons
So how exactly does it work? It’s actually quite simple: the sunlight passes through a small circular opening in a stained glass window at the southern end of the transept (the part of the church at right angles to the nave) and forms a disk of light on the floor, which crosses the meridian line when the sun is overhead at noon.
Depending on the time of year and the sun’s exact position in the sky, the disk of light is projected onto different parts of the meridian line, at one end of which stands an obelisk whose top is illuminated when the sun is at its lowest annual midday angle of elevation (during the winter solstice). Did you get all that?
However it’s not because of a passion for astronomy that tens of thousands of tourists flock to the church to see the gnomon. In fact it owes its popularity to a famous book, Dan Brown’s “Da Vinci Code”. Never short of fanciful suppositions, the American novelist described the obelisk as dating from Ancient Egypt and maintained that the meridian line was in fact a vestige of a pagan temple that had once stood on the site. Dan Brown aficionados call it the Rose Line and mistakenly equate it with the Paris meridian, which actually runs through Paris Observatory, serving as a reference for maps of Paris.
Of course none of the stuff in the novel is actually true, however the church and its gnomon are well worth the visit, even if it’s just to eavesdrop on the visitors as they expound on what they see as a French (conspiracy) Theory.
2 Rue Palatine, 75006 Paris
9 minutes walk from French Theory