Definition of Twilight

Definition of Twilight  

With some relief that the Inland Northwest has received a normal ration of snow, we can look forward to composing images for the Winter Scene at Twilight subject for March.  But what is twilight? Harvey Brown submitted a clear definition:

twilight: the light from the sky between full night and  sunrise or between sunset and full night produced by diffusion of sunlight through the atmosphere and its dust.

There are 3 stages of twilight that occur before sunrise or after sunset as follows:

  1. Civil:  30-35 min. after sunrise/sunset
  2. Nautical:  Next 40 min. after Civil
  3. Astronomical:  Next 40 min. after Nautical

Considering the above, twilight encompasses a period of nearly 1½ hours before sunrise or after sunset.  Although the Civil period will probably be the most workable, the continuation of  the remaining phases of twilight  may lend opportunity for some interesting photography.

An example of twilight phases for March 21, 2016:

  • 00:00—05:04 — night
  • 05:04—05:42 — astronomical twilight
  • 05:42—06:18 — nautical twilight
  • 06:18—06:49 — civil twilight
  • 06:49—06:52 — sunrise
  • 06:52—19:00 — daylight
  • 19:00—19:04 — sunset
  • 19:04—19:34 — civil twilight
  • 19:34—20:11 — nautical twilight
  • 20:11—20:48 — astronomical twilight
  • 20:48—00:00 — night

You can find timings for any location/date at http://www.timeanddate.com/astronomy/

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