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.)
Light Up Your Language for the Festival of LightsRead more in this article about some frequently asked questions and fun facts related to our definitions.
Words Built For SpeedRead more in this article about some frequently asked questions and fun facts related to our definitions.
- speed indicator,
- speed light,
- speed limit,
- speed metal,
- speed networking,
- speed ramp,
- speed shop,
- speed skate,
- speed skating,
- speed trap
A light year, or the distance light can travel in a year, is over five trillion miles.
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.
The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.