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Why isn't a shadow formed when a bird is flying in the sky?
- shruti nair (age 17)
The Sun isn’t just a single dot, but is somewhat spread out. That makes the shadows that form somewhat spread out. Think of the rays coming from one part of the Sun to the bird, and then to the Earth. They’ll form a shadow shifted a little from the one formed by rays from another part of the Sun. When the bird is high enough, these shadows are shifted enough from each other that no spot on the ground is in all the shadows. So the resulting shadow is very faint and hard to see. Roughly speaking, that happens when the bird is about 100 times as high as its own size.
(published on 10/22/2007)
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