Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio.
unwanted light in the night sky, as from city lights, that makes it more difficult for astronomers to see and photograph celestial objects
Used by arrangement with John Wiley & Sons, Inc.
nounThe American Heritage® Dictionary of the English Language, 4th edition Copyright © 2010 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Illumination of the night sky by electric lights, as in an urban area, that interferes with astronomical observation.