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Twilight In general use, that time period between daylight and darkness. It is used more precisely in celestial navigation since star sights must be taken during this period. Specific twilight times are often used in navigation jargon to refer to beginning and end of twilight periods. There are formally 3 types of twilight periods defined, and they are each defined according to the location of the sun at their darkest limit. The brighter limit of each period is either sunrise or sunset. Civil twilight ends when z = 96°, nautical twilight ends when z = 102°, and astronomical twilight when z = 108°, although we do not use the concept of astronomical twilight in routine cel nav. See Civil Twilight and Nautical Twilight.

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