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Re: shortest twilight problem...
From: Marcel Tschudin
Date: 2010 Jun 29, 20:55 +0300
From: Marcel Tschudin
Date: 2010 Jun 29, 20:55 +0300
John, Earlier on you wrote: "I think the change in declination around the equinoxes is a much smaller effect. That's a few minutes per day, so the fractional change in declination during the period of twilight will be a few seconds at most." Here your focus must have been on mid-latitudes; as mine when I concluded: "... it's thus a pure geometrical feature." You indicated then that there are some interesting limiting cases and mentioned the Poles. Indeed. At the Poles the length of the day is governed by the change in declination and therefore also the length of twilight. The length of the twilight is thus not only related to the latitude and the day but also to the declination. The latter becomes more and more important as one approaches the Poles. It's therefore not a "pure" geometrical feature, but may be rather a "dominantly" geometrical feature. Marcel