Every year during the summer solstice a remarkable astronomical event can be observed inside Florence’s Cathedral.
Between 12.30 pm and 1.30 pm on 21 and 28 June, the sun’s rays, falling through Brunelleschi’s Dome, projects the image of the solar disk perfectly overlapping onto the circular marble plate on the floor of the Chapel of the Cross, to the left of the High Altar. The event only lasts a few minutes.
Occurring every year since 1475, this phenomenon is due to an ancient astronomical instrument known as a gnomon (gnomone), a bronze tablet with a small opening, designed to measure the position of the sun in the sky and determine the duration of the calendar year. The gnomom is placed in the south window of the dome, 90 meters above the floor.
Entrance to the Cathedral to attend the event is free, but plan to arrive early.
