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Related to astronomical: Astronomical twilight, Astronomical Unit
Of or pertaining to astronomy or to observations of the celestial bodies. Also known as astronomic.
equinoctial, natural, or solar year. It contains one complete cycle of seasons.
The period of incomplete darkness following sunset and preceding sunrise. Twilight is designated as civil, nautical, or astronomical, as the darker limit occurs when the center of the sun is 6°, 12°, and 18°, respectively, below the celestial horizon. The period of civil twilight before sunrise is known as morning civil twilight and after the sunset as evening civil twilight. The air almanac lists the local mean times of the beginning of morning civil twilight and the end of evening civil twilight in exactly the same format as sunrise and sunset tables. The twilight tables are printed on the right-hand pages facing the sunrise and sunset tables, with each pair covering the same block of calendar dates.