speed of light

Cultural Dictionary

speed of light definition

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.
The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
Cite This Source
Explore Dictionary.com
Previous Definition: spectrum
Next Definition: sperm
Words Near: speed of light
More from Thesaurus.com
Synonyms and Antonyms for speed of light
More from Reference.com
Search for articles containing speed of light
More from Dictionary.com Translator
Dictionary.com Word FAQs

Dictionary.com presents 366 FAQs, incorporating some of the frequently asked questions from the past with newer queries.

Copyright © 2015 Dictionary.com, LLC. All rights reserved.
  • Please Login or Sign Up to use the Recent Searches feature