Dusk refers to the period of time following sunset. Although commonly confused with twilight, dusk is the time frame that occurs either before or after a twilight - when the sky is still generally bright and blue, but there is no sun to accompany it.
Civil dusk is the time at which the sun is 6 degrees below the horizon in the evening. At this time objects are distinguishable and some stars and planets are visible to the naked eye.
Nautical dusk is when the sun is 12 degrees below the horizon in the evening. At this time, objects are no longer distinguishable, and the horizon is no longer visible to the naked eye.
Astronomical dusk is the time at which the sun is 18 degrees below the horizon in the evening. At this time the sun no longer illuminates the sky, and thus no longer interferes with astronomical observations.
Dusk should not be confused with sunset, which is the moment when the trailing edge of the Sun itself sinks below the horizon.
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Last updated on Sunday October 05, 2008 at 15:31:49 PDT (GMT -0700)
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