Every summer solstice, between 12:30 and 13:30, a miraculous astronomical event takes place in the Cathedral. Just as it has done every year since 1475, in fact, the sun penetrates the gnomonic aperture at the base of the lantern, and eventually reaches the marble disc that stands on the multicoloured marble Cathedral floor. Designed by the great mathematician Paolo dal Pozzo Toscanelli, and restored by father Leonardo Ximenes in 1754, the Duomo sundial - which those present will be able to see in action, with their own eyes - still functions perfectly, despite being the oldest in the world still to function. Found 90 metres above the ground, it determine the duration of the solar year with impeccable accurace, and all without eating a single byte...This phenomenon can be seen by the public in the Cathedral's della Croce chapel, to the left of the Main Altar.