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 » Online Classroom   » Tech Support   » StarPilot   » Twilight times at high latitudes

Author Topic: Twilight times at high latitudes
 vjwilliams posted November 29, 2002 02:05 PM                   Twilight times at high latitudesAt the start of morning nautical twilight the sun has risen to a point that is some 12° below the horizon. At the start of morning civil twilight it has reached the point of being some 6° below the horizon. At high latitudes in some seasons, however, the sun might not ever get far enough below the horizon to cross one of these defining times. In these cases there are no beginnings of twilight. If your computation coincides with these circumstances, we present this fact in the calculator versions of StarPilot by setting the corresponding "twilight time" answer to the same as the rise or set time. (We are forced to this convention because we can only enter numbers in the calculator output fields and we believe that 00:00:00 is not as good a choice since this is an unlikely but still possible correct answer, whereas the convention we use is unambiguous.) Hence if you get the answer: nautical/civil/rise = 04:15:23, 03:44:12, 04:15:23, it means there is no nautical twilight (sun did not descend more than 12° below the horizon), civil twilight is 03:44:12 (sun did go at least 6° below), and then it rose at 04:15:23 — in whatever time zone you had set in the StarPilot. Likewise, 04:15:23,04:15:23,04:15:23, has the corresponding meaning that there was no nautical nor civil twilight.

 All times are Pacific