SCIENCE PHOTO LIBRARY SCIENCE PHOTO LIBRARY
Newton's sundial. Engraving of a sundial inscribed by English astronomer Isaac Newton (1642-1727) in his youth on a wall of his family's home, Wools- thorpe Manor. Sundials measure time by monitoring the position of the shadow of the stick projecting from the wall. This shadow moves across the face of the sundial as the Sun moves across the sky. This sundial has the time in Roman numerals around its outside, ranging from 5 o'clock in the morning to 5 o'clock in the evening. It is decorated with signs of the zodiac. A calendar is along its bottom edge.
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