Astronomical twilight: The time when the Sun is 12-18 degrees below the horizon.
Astronomical Twilight When the centre of the Sun is between 12º and 18º below the horizon; faint stars become visible.
Astronomical Unit (AU) The mean distance from the Earth to the Sun, i.e. 149,597,870 km or 499.005 light seconds.
Astronomical Twilight
The period from sunset to the time that the Sun is 18° below the horizon; or the corresponding period before sunrise.
Astronomical Unit ...
Astronomical Twilight -- For technical definition, please follow this link to the U.S. Naval Observatory Astronomical Applications website.
astronomical twilight: -12º and -18º
These values reflect the need for decreasing light levels for various activities.
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astronomical twilight (NASA SP-7, 1965) See twilight. astronomical unit (NASA SP-7, 1965) (abbr AU)
1. A unit of length, usually defined as the distance from the earth to the sun, 149,599,000 kilometers.
Analemma, Annular Eclipse, Anticrepuscular Ray, Aphelion, Astronomical Twilight, Astronomical Unit, Atmospheric Phenomena, Babcock's Dynamo Hypothesis, Carrington Rotation Number, Chromosphere, Circumzenithal Arc, Civil Twilight, Conjunction, Corona, ...
The zodiacal light appears as a faint triangle of light pointing upwards from the horizon, appearing after astronomical twilight (a little over an hour after local sunset, depending on your latitude) since it is overwhelmed by scattered sunlight in ...
Twilight - astronomical Astronomical twilight ends (in the evening sky) or begins (in the morning sky) when the Sun is 18° below the horizon.
Twilight - civil Civil twilight ends or begins when the Sun is 6° below the horizon.
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The longitude and latitude of a point on the Earth relative to the geoid. These coordinates are influenced by local gravity anomalies. see Zenith; Longitude, Terrestrial; Latitude, Terrestrial) [S92]
Astronomical Twilight ...
 See also: Twilight, Light, Atmosphere, Planet, Period
  
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