The period of time at which the sun is halfway between beginning morning and nautical twilight and sunrise, when there is enough light to see objects clearly with the unaided eye. At this time, light intensification devices are no longer effective, and the sun is six degrees below the eastern horizon. Also called BMCT.
BEGIN MORNING CIVIL TWILIGHT
Meaning of BEGIN MORNING CIVIL TWILIGHT in English
DOD English dictionary of military terms. Английский словарь военных терминов DOD. 2012