Geometry and the Restoration of Ancient Sundials: Camera Obscura Sundials in Cava de’ Tirreni and Pizzofalcone

Sundial is a special solar device which signals exclusively, every day of the year, when the Sun crosses the local meridian, at South, thus working as a perpetual calendar on which you can read the date, rather than the daily time. ‘Camera obscura sundials’ are traditionally housed in monumental architectures and are defined by two elements, in strict geometrical correspondence between them: the data line - marking on the floor the north-south direction - and the gnomonic hole that coincides with a small hole of circular shape, dug along one facades of the building, through which a star of solar rays enters, projecting, along the aforesaid graduated straight line, a small luminous ellipse on the floor. Sundials are the graphic evidence, on the ground, of complex astronomical projective events: to build them, frequently, there was the convergence of various doctrines, from mathematics to physics, geography, cartography, from geometry to art. In the Campania region, several sundials of great artistic and scientific value were built, but they are not adequately appreciated, due to the progressive loss of this ancient millenary culture, related to the measurement of time before the advent of modern watches. Ruined by negligence but also by the inability to carry out adequate restorations, they are a precious cultural heritage to be urgently saved, providing actions for the protection and the recovery, but also for the dissemination of their knowledge, that is likely to disperse definitively, as well as rapidly. The research focuses on two inactive sundials in Cava de 'Tirreni (SA) and Pizzofalcone (NA) proposing an original gnomonic instrument, able to adapt itself to any type of relationship between the facade (along which the gnomonic hole should be recreated) and the sundial on the floor.