Summer Solstice at the Cathedral of Santa Maria del Fiore

For a few days each year, inside the Cathedral of Santa Maria del Fiore, it is possible to observe the passage of the sun through the gnomic hole located at the top of Brunelleschi's dome.
The gnomon, also known as the "bronzina", is a bronze panel with a small hole approximately 5 cm in diameter, located 90 meters above the ground on the cathedral's lantern, which makes it the tallest instrument of its kind in the world.
The tiny hole projects a much wider beam of light, which moves across the cathedral's marble floor until marking the solstitial marker, a marble disk in the floor of the Tribuna Della Croce.
This instrument, which transforms the Cathedral into an astronomical observatory, was conceived in the 15th century by the mathematician and astronomer Paolo dal Pozzo Toscanelli. Thanks to this projection, it was possible to study the apparent motion of the sun and determine the solstice, the maximum altitude of the sun in the sky at midday during the year, and, consequently, the length of the year itself.
By studying the ratio between the height and diameter of the hole, a pinhole solar image was obtained, capable of showing sunspots, the progression of ongoing eclipses, or the passage of Venus between the sun and the Earth.
This exceptional instrument offers a highly evocative spectacle during the summer solstice, so much so that it has become a tradition for Florentines to go and observe the sun's movement across the cathedral floor during this period.

This year, the phenomenon was visible to the public on June 12th and will be visible again on June 19th from 12:30 pm to 1:30 pm. Admission is free, but reservations are required (subject to availability).