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Gnomon of Saint-Sulpice
The Gnomon of Saint-Sulpice is an astronomical measurement device located in the Church of Saint-Sulpice (Église Saint-Sulpice) in Paris, France. It is a gnomon, a device designed to cast a shadow on the ground in order to determine the position of the sun in the sky. In early modern times, other gnomons were also built in several Italian and French churches in order to better calculate astronomical events. Those churches are Santa Maria del Fiore in Florence, San Petronio in Bologna, and the Church of the Certosa in Rome. These gnomons ultimately fell into disuse with the advent of powerful telescopes.
The gnomon of Saint-Sulpice is composed of different parts that span the breadth of the transept of the church. The church itself is a huge building, the largest church in Paris.
The system is first built around a meridian, a line which is strictly oriented along the north-south axis, represented by a brass line set in a strip of white marble on the floor of the church. This is not the Paris Meridian, established by Louis XIV in 1667, which is located a few hundred metres to the east and goes through the Paris Observatory.
The sunlight passes through a small round opening in the southern stained-glass window of the transept, at a height of 25 metres, forming a small light disc on the floor; this disc will cross the meridian each time the sun reaches its zenith at true noon. The sun will cross different parts of the meridian depending the time of year, as the sun will be more or less high in the sky at noon. A point on the meridian is marked with a gold disc which shows the position of the sun at an equinox. It is located right in front of the altar.
At one end of the meridian is a square marble plaque, which corresponds to the position of the sun at the highest at midday (64°35' at the location of Saint-Sulpice), during the summer solstice about 21 June.
At the other end is an obelisk, which is lit near its top when the sun is at it lowest at midday (17°42' at the location of Saint-Sulpice). If the obelisk did not exist, the sun disc would hit an area about 20 metres beyond the wall of the church.
The gnomon was built at the initiative of Jean-Baptiste Languet de Gergy, the parish priest at Saint-Sulpice from 1714 to 1748. Languet de Gergy initially wished to establish the exact astronomical time in order to ring the bells at the most appropriate time of day. For this, he commissioned the English clockmaker Henry Sully to build the gnomon.
The gnomon could also have been used to properly time clocks by properly defining mean time. Mean time (the time used in clocks) is only an average of true time (the time deduced from the apparent motions of the Sun in the sky, and shown, approximately, by a sundial). True time deviates from the mechanical average of a clock by as much as +/-16 minutes throughout the year. These variations are codified in the equation of time. Henry Sully, however, died in 1728 without being able to accomplish this larger project. He was only able to set the meridian line in the floor of the Church. The project was completed by the nearby Paris Observatory a year later.
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Gnomon of Saint-Sulpice AI simulator
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Gnomon of Saint-Sulpice
The Gnomon of Saint-Sulpice is an astronomical measurement device located in the Church of Saint-Sulpice (Église Saint-Sulpice) in Paris, France. It is a gnomon, a device designed to cast a shadow on the ground in order to determine the position of the sun in the sky. In early modern times, other gnomons were also built in several Italian and French churches in order to better calculate astronomical events. Those churches are Santa Maria del Fiore in Florence, San Petronio in Bologna, and the Church of the Certosa in Rome. These gnomons ultimately fell into disuse with the advent of powerful telescopes.
The gnomon of Saint-Sulpice is composed of different parts that span the breadth of the transept of the church. The church itself is a huge building, the largest church in Paris.
The system is first built around a meridian, a line which is strictly oriented along the north-south axis, represented by a brass line set in a strip of white marble on the floor of the church. This is not the Paris Meridian, established by Louis XIV in 1667, which is located a few hundred metres to the east and goes through the Paris Observatory.
The sunlight passes through a small round opening in the southern stained-glass window of the transept, at a height of 25 metres, forming a small light disc on the floor; this disc will cross the meridian each time the sun reaches its zenith at true noon. The sun will cross different parts of the meridian depending the time of year, as the sun will be more or less high in the sky at noon. A point on the meridian is marked with a gold disc which shows the position of the sun at an equinox. It is located right in front of the altar.
At one end of the meridian is a square marble plaque, which corresponds to the position of the sun at the highest at midday (64°35' at the location of Saint-Sulpice), during the summer solstice about 21 June.
At the other end is an obelisk, which is lit near its top when the sun is at it lowest at midday (17°42' at the location of Saint-Sulpice). If the obelisk did not exist, the sun disc would hit an area about 20 metres beyond the wall of the church.
The gnomon was built at the initiative of Jean-Baptiste Languet de Gergy, the parish priest at Saint-Sulpice from 1714 to 1748. Languet de Gergy initially wished to establish the exact astronomical time in order to ring the bells at the most appropriate time of day. For this, he commissioned the English clockmaker Henry Sully to build the gnomon.
The gnomon could also have been used to properly time clocks by properly defining mean time. Mean time (the time used in clocks) is only an average of true time (the time deduced from the apparent motions of the Sun in the sky, and shown, approximately, by a sundial). True time deviates from the mechanical average of a clock by as much as +/-16 minutes throughout the year. These variations are codified in the equation of time. Henry Sully, however, died in 1728 without being able to accomplish this larger project. He was only able to set the meridian line in the floor of the Church. The project was completed by the nearby Paris Observatory a year later.