A memorial stone affixed to the Loggia dei Lanzi, in Piazza della Signoria, recalls as a historically significant moment the date on which in Florence too, at the decree of Grand Duke Francesco II of Lorraine, time began to be measured starting from January 1st of each year. It was 1750, the year in which the "Florentine style" calendar was definitively abandoned in favor of the one reformed by Pope Gregory XIII in 1582. Before 1750, the Florentine year began ab Incarnatione, on March 25, the day consecrated by the Catholic Church to the Archangel Gabriel's annunciation to Mary (nine months prior to the birth of Jesus). That date also coincided with the beginning of spring, which started only a few days earlier, on March 21, when the Sun entered the constellation of Aries. For Florence, this was a particularly important moment. It was the beginning of a new life marked on the astronomical level by the first season of the year, on the religious level by the festival of the Annunciation - grandiosely honored in the Church of the SS. Annunziata since the 13th century - and on the level of the city's origins, by the ancient Ludi Florales dedicated to Flora, the goddess of springtime, for whom Florence had been named. Two masterpieces by Botticelli, The Birth of Venus and the Primavera, have indelibly engraved in the collective consciousness the iconography of Flora-Florentia associated with the birth that recurs each year under the sign of Aries.
Another association links Florence to this astronomical moment. In astrology, the constellation of Aries is dominated by the planet Mars, and the god of war, up to the 5th century, was the protector of the ancient Roman city that originated as a military outpost. To Mars was dedicated the octagonal temple that was later to become, with the Christianizing of the city, the Baptistery of San Giovanni. The Christian transformation of the building was greeted in an astronomical key by the construction of the city's first monumental sundial. Each year on the day of the solstice, June 21, a sunbeam fell from the oculus in the cupola, open as in the Pantheon, to light up a zodiacal plaque set in the floor near the north door. A few days later came the Feast Day of St. John, June 24.
From the 15th to the 18th century, at least eight monumental gnomons were constructed, for scientific or commemorative purposes, in some of the city's most important buildings: the gnomon in Santa Maria del Fiore, built by Paolo dal Pozzo Toscanelli to measure the declination of the Sun at the summer solstice, and remodeled by Leonardo Ximenes to study the obliquity of the ecliptic; the astrological cupolas of San Lorenzo and the Pazzi Chapel, painted to fix the date of an important historical moment; the 'gnomon' of Santa Maria delle Carceri in Prato, constructed to celebrate each year the date of the miraculous event that took place there; the gnomons on Santa Maria Novella, constructed by Egnazio Danti in relation to the reform of the calendar; the now-lost gnomon of the Uffizi, built at the order of Ferdinando I, perhaps with a commemorative and symbolic intention; and the gnomon of La Specola, constructed for astronomical purposes in the grand-ducal observatory at the Museum of Physics.
The occasion for an exhibition dedicated to these monuments to astronomy is provided by the installation of a new Florentine sundial scheduled to enter operation at the next summer solstice, in Piazza dei Giudici, before the entrance to the Museum of the History of Science. With the aim of presenting to a larger public the illustrious precedents of this singular 'street furnishing', the exhibition will unfold in an ideal itinerary through the city of Florence to visit the places of gnomons, illustrating with models, graphic designs, projections and originals, the history of these extraordinary testimonials of time. The ideal itinerary can of course be transformed into a real one, facilitated by the presence of explanatory panels next to the buildings in which the sundials are located. The new sundial in Piazza dei Giudici will have no properly scientific function - very different instruments for measuring time and for astronomical observation are available today - but will serve a purpose that is educational, for young people especially, and in some way commemorative as well. Its installation coincides with the last summer of the 'old' museum, which at the next winter solstice, or thereabouts, will close its doors for nearly a year, with the promise of reopening them fully renovated for the beginning of the now imminent Galilean celebrations, in the spring of 2009, when the Sun enters the constellation of Aries once again.