NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: shortest twilight problem...
From: John Huth
Date: 2010 Jun 29, 08:43 -0400
From: John Huth
Date: 2010 Jun 29, 08:43 -0400
Marcel -
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. On the other hand the inclination angle of the sun wrt the horizon at the solstices versus other times should be a much larger factor.
John H.
On Tue, Jun 29, 2010 at 8:32 AM, Marcel Tschudin <marcel.e.tschudin@gmail.com> wrote:
George, you were correct. The longest duration of twilight at given
location is at a solstice, more precise at the summer solstice. I made
a quick calculation for a location at about 41 deg North, the observer
is 2m a.s.l., the atmospheric data are kept constant to standard 10C
and 1010hPa. The result is as shown in the attached graph. I still
have to understand why my reasoning which leads to the spring equinox
is wrong.
Marcel
