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## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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GHA Aries and GHA and Declination of the Sun
From: Bill Murdoch
Date: 1997 Dec 17, 9:35 PM

```Woops.  There is a mistake in the date part of the GHA Aries and sun GHA and
declination calculation forms that I posted a week or two ago.  I slipped up.
The year 2000 is a leap year, so an extra day of 86,400 seconds has to be
inserted after February 29.  I modified the form and a new copy is attached.
If you find any other mistakes, let me know.

For someone who wants to put the formulas a program, there is an easy way to
convert customary time and date to centuries before and after 1200 1 Jan 2000.
It comes from Van Flandern and Pulkkinen, Low Precision Formulae for Planetary
Positions, The Astrophysical Journal Supplement Series, vol 41, p 391, (1979).
It works from March 1900 through February 2100.  They also have another
formula for longer lengths of time.

T = (367*yr-trunc(7*(yr+trunc((mo+9)/12))/4)
+trunc(275*mo/9)+day+(hr+(min+sec/60)/60)/24
-730531.5)/36525

The function trunc is just like trunc in Excel.  It drops the fractional part
of the number.
trunc(8.9) = 8,
trunc(-8.9) = -8.

Bill Murdoch
Kingsport, Tenn.
```
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