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Subject: Re: September Equinox computation
From: Jay Borseth (jaybo@XXX.XXX)
Date: Wed Sep 25 2002 - 02:11:46 EDT
Sorry, pilot error!
The result I gave earlier using Pocket Stars was totally wrong. I
stupidly just searched for a declination of 0, without simultaneously
searching for SHA=180 deg.
The new, improved Pocket Stars result is: 4:55:26 AM GMT on 23 Sep
2002, crossing at E 104d16.8'.
I don't know for sure, but I'm guessing the 2 second discrepancy could
be due to differences in DeltaT, for which I've seen multiple different
projections for 2005. Values for intermediate dates such as 23 Sep 2002
are linearly interpolated from the 2000 and 2005 data points. Pocket
Stars is using 69 seconds for 2005, but I've seen 66 seconds used
elsewhere.
...
Julian Date Year DeltaT
2451544.5000000, /*2000.0000,*/ 63.86,
2453371.5000000, /*2005.0000,*/ 69.0, // 66. Alternate values from
other sources
2455197.5000000, /*2010.0000,*/ 74.0, // 70.
...
Jay Borseth
> Herbert Prinz wrote:
>
> Hi guys,
>
> I was already wondering how Dan Allen could be off by more
> than 3 minutes using Meeus' algorithm, but no way did I
> believe that the JPL ephemeris plus Novas routines could be
> early by 3.5 minutes, whether its all written in Fortran, C or Cobol.
>
> So I plug the numbers into my carefully re-written Pascal
> version of the Novas routines using DE200 and obtain (by
> doing what I described in my earlier message) for the time of
> this year's autemnal equinox 4:55:24 UT1. This value has the
> advantage that it agrees with what Meeus publishes in "Tables
> of the Sun, Moon and Planets", as well as with what the USNO
> thinks it should be. (see Earth's Seasons, etc. 1992-2005
> ). This is probably not a coincidence.
>
> Herbert Prinz
>
> >
> > Jay Borseth wrote:
> >
> > The results I'm getting put the equinox at:
> >
> > 4:51:54 AM GMT on 23 Sep 2002, crossing at E 105
> degrees 9' 56".
> >
> >
> > Dan Allen wrote:
> >
> > PS - My computations for this year put the equinox at
> 4:52:04 AM GMT
> > on 23 Sep 2002.
>
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