Apart from measuring the position of the sun in the sky within half a second, the gnomon helped indicate the best times in the year to sow and harvest as well as working out the sun’s yearly path through the stars. It was eventually replaced in general use by the telescope, but despite technological advances it’s still an accurate and simple device that was an essential tool for the time.
Dating back to the fifteenth century it is still remarkably accurate. The gnomon was first used in 1475, as documents found in the archive of the Opera of Santa Maria del Fiore suggest, and it was restored 300 years after its construction in 1754 by Jesuit priest, Leonardo Ximenes, making it one of the oldest pieces of astronomical kit in the world.
To mark the occasion the Duomo opens its doors to the public to admire the spectacle between 12.30 pm and 1.30 pm on the day of the summer solstice. Free entrance but booking is recommended.