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Dear Frank,
if you are interested I tested Deneb, Aldebaran, and Polaris  on Dec 1� 1770 
(6 GMT) using my software based on Swiss Ephemeris and Moshier Epehmeris. I 
used it very satisfactorily for the last three years with continuous 
testing.
I found the following results very close to those of the stellarium:
Deneb         44d 28' 36"
Aldebaran    16d 01' 47.4"
Polaris        88d 05' 16.8"
Of course if any one would like to try, I will be happy to distribute it
Giuseppe
----- Original Message ----- 
From: "Frank Reed" 
To: "NavList" 
Sent: Friday, December 01, 2006 9:21 AM
Subject: [NavList 1797] Re: Stellarium and the heavens in the 17th century


>
> Nicolas, you wrote:
> "Does anyone of you know Stellarium (http://www.stellarium.org/) and
> how
> accurate it is for long gone years? "
>
> First, that is one very fine piece of software --a really beautiful
> planetarium simulator. Thanks for bringing it up. This is the first
> time I've seen it.
>
> As for Stellarium's accuracy, it does not appear to be very high.
> Comparing positions for any date including current dates, I find
> typical errors of 30 seconds of arc. For example, at 0600 GMT on
> December 1, 2006, Stellarium gives the Moon's Declination as 09d 12'
> 21" while my Online Nautical Almanac (see my web site at
> www.HistoricalAtlas.com/lunars) has 09d 12' 42" (geocentric). I don't
> yet see a way in Stellarium to get geocentric coordinates directly so I
> extracted the Moon's Dec by travelling to that spot in the Pacific
> Ocean where the Moon was in the zenith. That nulls out the refraction
> and parallax. I can't think of any way to explain away a discrepancy of
> 21 seconds of arc. That's a large error by the standards of this type
> of software.
>
> For a few other cases, I went to December 1, 1770 at 0600 GMT. I find
> these discrepancies in declination:
> Object         Stellarium            my online almanac
> -------------------------------------------------------------------------
> Deneb         44d 28' 36"           44d 28' 23"
> Aldebaran    16d 01' 47"           16d 01' 11"
> Polaris        88d 05' 16"           88d 05' 16"
>
> I have extensively tested my own almanac output, which is based
> internally on the JPL ephemeris data for the Moon and planets and the
> Hipparcos positions and proper motions for the stars, and it can be
> trusted to the nearest second of arc. Based on these comparisons, it
> appears that you could certainly trust the Stellarium positions to one
> minute of arc (good enough for the vast majority of historical
> navigation problems), but you should not trust it for anything
> requiring higher accuracy (like lunars ).
>
> I should add that there is the possibility that the data displayed in
> Stellarium refers to some non-standard set of coordinates. So it may
> still be "correct" and accurate. The source code of Stellarium is
> available in the Linux download. There is one three megabyte block of
> code with "VSOP87" in the file name. This is a particular set of
> calculational algorithms for planetary positions, generally very
> accurate.
>
> If you want really high accuracy (for historical planetary positions in
> particular), I highly recommend "Solex" created by Aldo Vitagliano:
> http://chemistry.unina.it/~alvitagl/solex/. This is at the other end of
> the spectrum from Stellarium. It's extremely accurate over a very long
> time range, blowing away all the competition, but it has mostly plain
> text output.
>
> -FER
>
>
> >
> 


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