Each June, Florence Cathedral hosts a unique demonstration of nature's precision matched by human engineering: the passage of the midday sun through a gnomon set into the mighty dome. Unnoticed by visitors for most of the year, the Duomo's gnomon – a device that tells the time of day or year by the way the sun strikes it – comes into its own between late May and July each year.

The instrument itself is hard to spot: located just over 90 metres up, just beneath the windowed lantern at the top of the dome, it looks like a small bronze shelf jutting out from the southern wall. More easily identified is the brass meridian line running across the floor of the Chapel of the Cross, accompanied by an inlaid circle.