The Florence Duomo’s Gnomon, An Ancient Astronomical Tool

the solar disc moving across the floor of the Duomo of Florence

A very special way of marking the summer solstice takes place in Florence every year. For one hour at midday, on specific dates on and near the solstice, sunlight streams through the cupola of Santa Maria del Fiore, the Duomo of Florence, casting a disc shape in sunlight on the cathedral floor.  The mechanism by which this fascinating phenomenon works is known as the gnomon, specifically a pinhole gnomon, an ancient astronomical device that calculates the position of the sun in the sky.

As sunlight streams in through the hole in Brunelleschi’s dome, the solar disc moves across the church floor until it aligns exactly above a bronze inlaid disc. The highly accurate device, positioned at 90 meters above the church floor, is one of the oldest of its kind, having been created in 1475 by Florentine astronomer Paolo dal Pozzo Toscanelli.

For 2017, the phenomenon can be witnessed on June 21, 27, and 28, from 12:30 to 1:30. The event is free and open to the public, but reservations are recommended. Contact the Opera del Duomo at +39 055 230 2885.

And why not join our Original Florence Walk to learn more about the Florence Duomo, its fascinating history, art and architecture!

(Photos courtesy of Sestini and Duomo Opera)

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