A heliograph is a simple instrument that is used to measure the length of sunlight, but not the intensity of the sun’s radiation. Its main component is a glass sphere that acts as a lens – a coupler that concentrates the rays into one spot, so that a trace is burned onto a measuring tape placed behind the lens ( source: wikipedia).
A commonly used heliograph includes a 10 cm diameter sphere made of annealed optical glass.
Our heliograph is also unique in that the sphere is 26 cm in diameter. The base was made by the artistic blacksmith Mr. Miroslav Liederhaus.
