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

Abstract

Today restoring ancient “camera obscura sundials” by drilling holes in building façades appears as an overly intrusive intervention in historical architecture. For this reason, our study proposes an innovative, low-cost gnomonic instrument, capable of adapting to any type of relationship between the façade where the original gnomonic hole was located) and the sundial on the floor. The tool that we have designed allows incoming sunlight to be caught by a reflection system of flat mirrors, appropriately tilted, thus producing a solar ray that exits the instrument with a different inclination. We created new angular relationships between the gnomonic hole and the astronomic data engraved along the sundial in two case studies of historic sundials that are now inactive and abandoned. The research was conducted weaving astronomy and gnomonics with geometry and mathematics, to create a 3D model to verify, plan and execute the restoration of historic sundials.