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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: When did the Atumnal Equinox occure this year?
From: Brad Morris
Date: 2019 Sep 27, 14:15 -0400
From: Brad Morris
Date: 2019 Sep 27, 14:15 -0400
Hello Peter
Have you examined Paul's results for this particular exercise?
I knew, once the question came up, that a variety of answers would be forthcoming. Having been around NavList for a long time lends itself to some procedural understanding.
Paul Hirose has, at least to my eyes, the most accurate definition of the issue. His answer, elliptic longitude = 7:50:11, differs marginally from yours.
Perhaps the computation in the spreadsheet is missing some minor wobble of the earth's axis, or perhaps some other tweak is needed.
Brad
On Fri, Sep 27, 2019, 2:00 PM Peter Hakel <NoReply_PeterHakel@navlist.net> wrote:
Frank, you asked about the values of Sun’s SHA around the autumnal equinox this and the next year.
The attached spreadsheet displays the right ascension of the Sun (“Alpha” in cell A61), which works equally well as the SHA. For September 23, 2019 we have
UT = 07:49:58
Alpha = 179.9999899 degrees
UT = 07:49:59
Alpha = 180.0000003 degrees
which are the two times bracketing the change in declination sign reported in my previous post.
Delta T is computed to be 71.4 seconds (cell B16).
For September 22, 2020 I get
UT = 13:30:31
Alpha = 179.9999899 degrees
UT = 13:30:32
Alpha = 180.0000003 degrees
Delta T is 72.0 seconds. The declination sign change from N to S is bracketed by these two time instants as well.
Peter Hakel
