BASILICA di SANTA MARIA NOVELLA . FLORENCE – Danti’s Armillary Sphere – GAUDIUM SUB SOLE . SUNDIALS . MEDIEVAL TO MODERN

SANTA MARIA NOVELLA . FLORENCE . ARMILLARY SPHERE

EGNAZIO DANTI* 1536 – 1586 (also, Ignazio), Dominican monk and polymath, became renowned for his wide learning and intellectual precision. He was a mathematician, cartographer, astronomer (some say ‘cosmographer’) to Cosimo I, and much more. There’s plenty about him – and indeed about his 3 very different dials at SMN – online.

Recommended sites for an informed overview of the dial include that of the Basilica itself SMN.IT; also ARTELEONARDO and ACCADEMIAGALLERY

For those wishing to dig deep into the complex analysis and the historical context of the dial, you can do no better than study the lead article by Simone Bartolini & Marco Pierozzi in the BULLETIN OF THE BRITISH SUNDIAL SOCIETY VOLUME 22(iv) – December 2010. You can download it.

ARMILLARY SPHERE

The armillary sphere consists of two perpendicular bronze circles with a diameter of 1.30 cm. The vertical one represents the meridian and indicates the exact moment when the sun is at its highest point, noon. On the equinox day, these two circles create a cross-shaped shadow, while elongated circle shadows are formed on other days. (AG)

REFORMATION OF THE CALENDAR

Danti’s sphere was installed on the S facade of the SMN in 1572. This device enabled him to determine the equinox precisely, and thus the true length of the year. Measurements the following spring confirmed the conjecture that the equinox was earlier than indicated by the Julian calendar, in fact by 11 days. As Wiki (always good on this sort of topic) puts it: The reforms of Julius Caesar in 45 BC put the Roman world on a solar calendar. This Julian calendar was faulty in that its intercalation still allowed the astronomical solstices and equinoxes to advance against it by about 11 minutes per year. Pope Gregory XIII introduced a correction in 1582; the Gregorian calendar was only slowly adopted by different nations over a period of centuries, but it is now by far the most commonly used calendar around the world.