Between late November and mid-January the sun is so low that there is not even civil twilight, with the only exception from complete darkness being a deeper blue sky called " nautical twilight ", that occurs for a few hours in mid-day.
12.
At the winter solstice within the polar circle, twilight can extend through solar noon at latitudes below 72.561?( 72?32 433 ) for civil twilight, 78.561?( 78?32 433 ) for nautical twilight, and 84.561?( 84?32 433 ) for astronomical twilight.
13.
A civil twilight period of about two weeks occurs before sunrise and after sunset, a nautical twilight period of about five weeks occurs before sunrise and after sunset and an astronomical twilight period of about seven weeks occurs before sunrise and after sunset.
14.
This is followed by the nautical twilight, when the sun is 6?and 12?below the horizon ( heights of between " 6?and " 12?), after which comes the astronomical twilight, defined as the period from " 12?to " 18?
15.
Although Helsinki, Oslo, Stockholm, Tallinn, and Saint Petersburg also enter into nautical twilight after sunset, they do have noticeably lighter skies at night ( known as white nights ) around the summer solstice than other locations mentioned in their category above, because they do not go far into nautical twilight.
16.
Although Helsinki, Oslo, Stockholm, Tallinn, and Saint Petersburg also enter into nautical twilight after sunset, they do have noticeably lighter skies at night ( known as white nights ) around the summer solstice than other locations mentioned in their category above, because they do not go far into nautical twilight.
17.
At about 04 : 30, just before Nautical Twilight, the flotilla broke into two; one group of three LCAs continued on the same bearing toward Vasterival ( Orange One Beach ) and four LCAs followed MGB 312 to a new bearing starboard along the coast to Quiberville ( Orange Two Beach ).
18.
:Though not directly relevant to the question, the uncertainty of the boundaries of night and day is underlined by there being three differingly defined twilights : Civil twilight, Nautical twilight and Astronomical twilight, which begin or end when the Sun is 6, 12 or 18 degrees below the horizon respectively . { The poster formerly known as 87.81.230.195 } talk ) 13 : 24, 27 December 2016 ( UTC)
