Devised and created for the British Sundial Society by
Tony Moss BSc DLC
“The Lindisfarne Presse”
Part 1. How Sundials Work.
From the earliest times people have regulated their lives by the apparent motions of the Sun and the shadows cast by its rays. We say ‘apparent’ because of course it is the rotation of the Earth on its axis which causes the moving shadows we observe every day. When the Earth rotates 15° it is just as though the Sun had moved 15° around its daily track. Diallists use both conventions but it is usually easier to regard the Sun as being in motion.
Perhaps the best place to begin an understanding of how sundials work would be to imagine a pictorial view of the Earth at the North Pole In this diagram it is the Sun which seems to move at 15° every hour. The shadow-casting element of a sundial is usually called the ‘gnomon’ of which the edges are its ‘styles’.