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1. Figuratively, a faint light.
2. Pertaining to faint or indistinct mental perception, as in twilight state.
[A.S. twi-, two]
Farlex Partner Medical Dictionary © Farlex 2012
References in periodicals archive ?
By the 26th, the date Mercury reaches greatest western elongation 18[degrees] from the Sun, the planet is brighter than zero magnitude and rises just before 5 a.m., right after the start of astronomical twilight.
However, it is worth noting that both cases of catches during astronomical twilight occurred on moonless nights.
Of those observations, 103 occurred during the day, 113 occurred at night, and 41 occurred during astronomical twilight. There were 50 total observations during the first 2 wk of the study (18-31 October).
Casual observers may see no difference between night and astronomical twilight, but astronomers know it's the best time for using telescopes, especially for viewing distant galaxies.
But by the end of the month this has increased to 11 hours with astronomical twilight arriving later and later.
Astronomical twilight ends when the Sun is 18[degrees] below the horizon.
The Sun sets at a near-vertical angle near the equator, so the time between sunset and astronomical twilight is quite short compared to mid-northern latitudes, and we were observing within 20 minutes.
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.
The Moon will be 22[degrees] high in the west-northwest sky, with the Sun 18[degrees] below the horizon (the end of astronomical twilight).
Uranus, in Pisces, transits the meridian at the end of astronomical twilight as 2015 ends.

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