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| speed of light | |
noun | |
| the speed at which light travels in a vacuum; the constancy and universality of the speed of light is recognized by defining it to be exactly 299,792,458 meters per second |
| WordNet® 3.0, © 2006 by Princeton University. |
Speed of light
To learn more about Speed of light visit Britannica.com
| © 2008 Encyclopædia Britannica, Inc. |
speed of light
The distance light can travel in a unit of time through a given substance. Light travels through a vacuum at about 186,000 miles, or 300,000 kilometers, per second. (See E = mc2, electromagnetic waves, relativity, and twin paradox.)
Note: A light year, or the distance light can travel in a year, is over five trillion miles.
Note: Light from the sun takes about eight minutes to reach the Earth.
Note: Light from the moon, and other electromagnetic radiation from the moon, takes about a second and a half to reach the Earth. In conversations between astronauts on the moon and their ground crews, there are lapses of about three seconds between exchanges, because of the time it takes for radio waves to make a round trip between the Earth and the moon.
Note: The special theory of relativity states that the speed of light as measured by all observers is the same.
[Chapter:] Physical Sciences and Mathematics
| The American Heritage® New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved. |
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