Conceptual Physics (12th Edition)

Published by Addison-Wesley
ISBN 10: 0321909100
ISBN 13: 978-0-32190-910-7

Chapter 26 - Think and Explain: 76


You see your hand "in the past".

Work Step by Step

Light has a large but finite speed. When you look at your hand, you are receiving the light that left your hand a short time ago. Divide the distance between your hand and your eye by the speed of light to calculate how far back into the past you are seeing. Example: light travels a distance of 30 cm in a billionth of a second. One rule of thumb is that light travels about a foot per nanosecond (actually, about 1.02 ns).
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