I went to Saint Sulpice in Paris. It is the third largest church in Paris and dates back to 1646. And lo and behold there was an obelisk in the church of which I have written before after seeing light pillars on my way to work, Perhaps it was an Ecumenical outreach to the Egyptian Sun God Ra. There is a small hole in the stained glass window opposite the obelisk that allows a small disk of light to fall on the floor. This functions as a gnomon. When the disk of light is at its highest point (measured in an arc across the floor) it is 12 Noon. https://en.wikipedia.org/wiki/Saint-Sulpice,_Paris
Everything turns on itself. I have seen light pillars over Long Island Sound in the Winter https://zenlogos.com/10-22-2018-light-pillar
The disk of light’s path (at 12 Noon) moves to a different position across the floor every day and that point is marked with a brass line. There are markers for the winter solstice (the gold ball on top of the obelisk), the summer solstice on the floor nearest the window and the equinoxes (on the alter). The gnomon was used to calculate time (12 N accurate to a second) and the date of Easter (the first Sunday after the first full moon after the Spring Equinox).
In Egyptian mythology, the obelisk symbolized the sun god Ra, and during the religious reformation of Akhenaten it was said to have been a petrified ray of the Aten, the sundisk. Benben was the mound that arose from the primordial waters Nu upon which the creator god Atum settled in the creation story of the Heliopolitan creation myth form of Ancient Egyptian religion. The Benben stone (also known as a pyramidion) is the top stone of the Egyptian pyramid. It is also related to the obelisk.
Both New York University Egyptologist Patricia Blackwell Gary and Astronomy senior editor Richard Talcott hypothesize that the shapes of the ancient Egyptian pyramid and obelisk were derived from natural phenomena associated with the sun (the sun-god Ra being the Egyptians’ greatest deity at that time). The pyramid and obelisk’s significance have been previously overlooked, especially the astronomical phenomena connected with sunrise and sunset: Zodiacal light and sun pillars respectively.
https://en.wikipedia.org/wiki/Obelisk
There is another church the famous Duomo di Firenze that I have written about before that has a gnomon as well.
https://zenlogos.com/the-gnomon-of-the-cathedral-of-santa-maria-del-fiore/