twilight

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Related to Astronomical twilight: astronomical year

twi·light

(twī'līt),
1. Figuratively, a faint light.
2. Pertaining to faint or indistinct mental perception, as in twilight state.
[A.S. twi-, two]
References in periodicals archive ?
In fact astronomical twilight (when the Sun is less than 18[degrees] below the horizon) lasts all night from May 24 to July 22 for those observing from the latitude of London (51[degrees] 30').
So much so that the skies never get truly dark at this time of year, and the sky remains in an astronomical twilight for what little of the night we have.
Astronomical twilight ends when the Sun is 18[degrees] below the horizon.

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