First Heliometer in Italy

The Perinaldesian passion for astronomy made possible the realization of a dream: a brand new dark-room sundial in the Madonna della Visitazione Sanctuary, a small church at little distance from the village, that the popular tradition pretended “orientated on the meridian, following Cassini’s directions.”

The actual orientation of the church is only 6°30′ relatively to the north-south axis, thus the realization of a meridian line throughout the whole nave was possible (also thanks to the elevation and position of the gnomonic hole).Perinaldo is a beautiful little town in the west ligurian hinterland, at an elevation of 572 m (1,677 ft) above sea level, at just 15 Km from the sea and 25 Km from Italy-France borders. It is the birthplace of the great astronomer Giovanni Domenico Cassini (1625-1712), whose most famous realization is probably the huge “heliometer” (or meridian line, or dark-room sundial) realized in 1655 inside the San Petronio Basilica in Bologna, still the biggest dark-room sundial in the world. The sanctuary dedicated to the Madonna della Visitazione date back to XVII century.

The particular orientation of the church, similar to the Bologna Basilica, gave the idea to build a dark-room sundial and to dedicate it to the Great Astronomer.The realization of this sundial was an amazing challenge: it required a huge amount of studies, calculations and tests. A wooden scale model of the church was handcrafted to check and show the sunlight path on the two-leveled floor.International experts were asked to give their astronomical or historical contributions. Funds were retrieved and permissions were given. One of the most difficult parts was the accurate cutting and meticulous installation of marble tiles, following the previous calculations.

During the year, day after day, it runs along the line between the two solstices: by the summer, when the sun is at its maximum height above the horizon, in the winter, when the sun is at its minimum height; real calendar, indeed astronomical almanac, given the large amount of data that the tool can provide many aspects of the apparent movement of the sun and the movements of the Earth: the values of the declination of the Sun every day of the year, obliquity the Earth’s axis, the change in the Sun’s apparent diameter.

The Italian and French Riviera and the Valleys

Heliometer or Dark-Room Sundial

Heliometer or Dark-Room Sundial

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