astronomical twilight


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Related to astronomical twilight: astronomical year

astronomical twilight

See twilight.

astronomical twilight

[‚as·trə′näm·ə·kəl ′twī‚līt]
(astronomy)
The period of incomplete darkness when the center of the sun is more than 6° but not more than 18° below the celestial horizon.

astronomical twilight

The period before sunrise and after sunset when sun's center is between 12° and 18° below sea-level horizon. This may be regarded for all practical purposes as synonymous with complete darkness.
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References in periodicals archive ?
koebelei at Wakulla Beach were found to fly during astronomical twilight (Table 3).
During January, Mars rises shortly before sunrise and is visible for less than half an hour before astronomical twilight ends.
At the beginning of astronomical twilight it's a respectable 20[degrees] up as seen by observers at 40[degrees] north latitude, but the waning gibbous Moon will brighten the sky.
The planet sets more than 1 1/2 hours after the Sun during the first half of April, lingering above the horizon just after the end of astronomical twilight (at 40[degrees] north latitude) for the only time this year.
Far-southerners can duck the waxing gibbous Moon on the morning of May 6th; at 30 [degrees] south latitude it sets more than an hour before the start of astronomical twilight.
Jupiter ends the month setting only 11/2 hours after sunset, near the end of astronomical twilight. But Jupiter finds a new close companion in December's final days.
During astronomical twilight, most people think that it's fully dark, but stargazers complain that the Milky Way looks washed out.
The best time to look is right after astronomical twilight, before Cetus gets too low.
The 12-minute exposure just after astronomical twilight produced one of the better photos of the zodiacal light I can recall.
You should begin observing the cluster before the end of astronomical twilight (when the Sun is 18[degrees] below the horizon).
On November 27th, around the start of astronomical twilight, telescope enthusiasts in much of eastern North America should be able to see the shadow of Ganymede projected as a black spot on the planet's disk.

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