This is New Year's Day according to the ancient calendar of Pisa. On March 25th every year, at noon, a ray of sun enters the cathedral passing through a south-facing window of the S.Ranieri chapel.

Every year on this day there are prayers and celebration on the steps of the cathedral and the musical performances inside. The Pisan calendar starting counting the days a full nine months before December 25th of the year zero.

The New Year started on March 25th and ended on March 24th the year after. The modern calendar of Europe is the Gregorian calendar which was implemented in 1582 by Pope Gregory XIII. It replaced the Julian calendar, which had been in use since the fourth century.

In Pisa, it fell out of use on December 31st, 1749, when the Grand Duke of Tuscany Francesco ordered all of Tuscany under the current Gregorian calendar. Until then, Florence also had its own calendar, similar to Pisa's, but one year behind.