astronomical twilight


Also found in: Dictionary, Thesaurus, Medical, Wikipedia.
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.
Mentioned in ?
References in periodicals archive ?
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.
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.
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).

Full browser ?