Twilight, was Re: I saw Mir! (& Cosmos 1953)

Bjoern Gimle (bjorn@tt-tech.se)
Tue, 26 Aug 1997 09:22:25 +0200

Ed Cannon (ecannon@mail.utexas.edu) wrote:
> sunset - 8:04 p.m. CDT (1:04 UT, 24 August)
> Mir - 8:23-24
> 10-deg. twilight - 8:48

>Glaring arithmetic error -- it was 25 minutes, not 15, before the 
>10-degree twilight time!

This needs more arithmetic - we don't all live on the same latitude.
Near the equator, Sun would be only -3.8 degrees from the horizon.
At my latitude, on July 23, 25 minutes means -9.6 deg.Sun elevation
(below -10 for 34 minutes), on Sep.22 it means -6.9 degrees.

When I use QuickSat I have to adjust my time limits according to
the season. Track16, SkyMap (and TrakStar) use 'Maximum Sun Elevation',
which has a constant meaning over the seasons, and the globe.

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