When the sun passes trough the Brunelleschi’s Cupola
In 1475 the Florentine Mathematics Paolo dal Pozzo Toscanelli built the gnomon, an astronomical indicator to measure the exact position of the sun. The sun penetrates the lantern’s window and passes trough the gnomon; then the sun’s rays pass trough a small bronze hole of just 4 centimeters in diameter and form a disk of light that hits the marble floor of the Duomo. Where the sun touches the floor inside the Chapel of the Cross, there is a meridian clock and a large marble disk, measuring 90 cm, that indicates noon time.
This astronomical magic happens all year round, but the most impressive phenomenon is during the Summer Solstice marking the highest point reached by the sun into the sky, as well as the longest day. This event used to be really important for Mathematics and Scholars in the past centuries to understand how and how long the Sun and the Earth move. The gnomon of the Duomo of Florence is the largest ever built in the world with a height of 90 meters.
The astronomical event happens every in 4 or 5 different days in June and always on June 21st, the Summer Solstice, between 12.30 and 1.30pm. Anyone can attend it and the event is free upon reservation by sending an email to email@example.com. The entrance is through the door of the Canonici, i.e. the door on the side of the Campanile. If you want to get a better seat I recommend to arrive at least 30 minutes before the event’s start.