Sundial, 16th century artwork. This shows how a vertical sundial works. The Sun (upper left) casts two shadows, one for the vertical slab and one for the horizontal rod. The combination of these shadows can be used to keep track of the time as the Sun moves through the sky. The text labels are in Latin, and include the word 'umbra' (shadow). This artwork is from the 1552 edition of Sphaera Mundi, by the French mathematician and cartographer Oronce Fine (1494-1555). Sphaera Mundi (Sphere of the World) was an astronomy textbook with woodcut illustrations by Fine. It was first published in 1542.