twilight, period between sunset and total darkness or between total darkness and sunrise. Total darkness does not occur immediately when the sun sinks below the horizon because light from the sun that strikes the atmosphere is scattered (both by the air itself and by suspended matter, e.g., dust and smoke). Civil twilight ends when the center of the sun is 6° below the horizon. Although it is still not very dark, it is necessary to use artificial light to carry out most activities. Nautical twilight ends when the sun's center is 12° below the horizon; at about this time the light is too dim for the user of a sextant to see a sharp horizon. Astronomical twilight ends when the sun's center is 18° below the horizon; by this time even the faintest stars overhead can be seen. (Similar definitions apply to morning twilight.) During twilight, Venus or Mercury is often seen as the evening star or morning star. The length of twilight depends on latitude and the time of year. Twilight is generally shorter at the equator, where the sun's path toward the horizon is more nearly vertical than at higher latitudes; typically, astronomical twilight may last for 1 hr at the equator and 11/2 hr in New York City.

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.

More on twilight from Fact Monster:

  • The Twilight Series - Read biographies of the actors in and reviews of the movies and books in Stephenie Meyer's Twilight series. Plus, take quizzes and polls about the series.
  • Twilight Trivia - Learn about the symbolism, origin of names, and other interesting tidbits in Stephenie Meyer's Twilight.
  • Twilight: Movie Review - Read this review of the movie Twilight, the first installment in Stephanie Meyer's best-selling series.
  • Twilight Quiz: 1 - How much do you know about Edward Cullen, Bella Swan, and the vampires that make up the best-selling Twilight by Stephanie Meyer? Take the quiz!
  • Hangman - Twilight - Twilight Try Another Click here for a our creature catalog. Program based on "Hangman" by ...

See more Encyclopedia articles on: Astronomy: General

Play Hangman

Play Poptropica

Play Quizzes

Play Tic Tac Toe