Astronomical Twilight: The time after nautical twilight has commenced and when the sky is dark enough, away from the sun's location, to allow astronomical work to proceed. It ends when the center of the sun is 18° below the horizon.

 

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Astronomical Twilight: The time after nautical twilight has commenced and when the sky is dark enough, away from the sun's location, to allow astronomical work to proceed. It ends when the center of the sun is 18° . . . View Full Definition

Twilight: Often called dusk, it is the evening period of waning light from the time of sunset to dark. The time of increasing light in the morning is called dawn. Twilight ends in the evening or begin . . . View Full Definition

Twilight Rate: A discounted green fee based on the fact that a limited number of holes may be completed due to darkness

Twilight Zone: See Mesopelagic Zone.

Lowest Astronomical Tide: As defined by the International Hydrographic Organization, the lowest tide level that can be predicted to occur under average meteorological conditions and under any combination of astronomi . . . View Full Definition

Civil Twilight: The time between the moment of sunset, when the sun's apparent upper edge is just at the horizon, until the center of the sun is 6° directly below the horizon.

Astronomical Time: Time formerly used in astronomical calculations in which the day began at noon rather than midnight. The astronomical day commenced at noon of the civil day of the same date. The hours of th . . . View Full Definition

Nautical Twilight: The time after civil twilight, when the brighter stars used for celestial navigation have appeared and the horizon may still be seen. It ends when the center of the sun is 12 degrees below t . . . View Full Definition