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Eclipse Shadows |
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| The sun is a disk rather than a point light source. Point source shadows are always sharp, sun-disk shadows change form with distance to the surface where they display. Close-up the shadow is the object's silhouette. Further away the dark shadow (umbra) develops a lighter edge (penumbra). Further still and no dark umbra remains. We have merely a penumbral blur. Place the eye anywhere in this penumbra and part of the sun will be visible. Top left is a simulation of a penumbral shadow. We usually do not notice them. Replace the solar disk by the thin crescent of an eclipse. Shadows become unfamiliar. In some directions the sun acts more like a point source and shadows become that much sharper and darker in some directions. The finger in the simulation is still recognisable. The crescent can be regarded as a arc of point sources. Each casts its own shadow. The overall shadow acquires crescent-like features. At left the finger tip has become a crescent shaped shadow and the hand claw-like. The hands in the images have taken on crescent-like qualities. |