[Kstars-devel] finding 'weird' celestial events

[Jason Harris]

Hi Steve,

This would be a really interesting use of a program like KStars, but I have to 
caution you to think very carefully about the uncertainties inherent in 
determining past eclipse events.

Determining the position of the Moon in the sky given a time and date is an 
incredibly complex problem.  In fact, there is no analytic solution to the 
problem (indeed, it has been proven that no analytic solution exists).  
Therefore, the best you can do is a numerical integration that approximates 
the Moon's position.  This numerical model is tuned to be accurate for modern 
dates, for which we have precise measurements of the Moon's position to check 
against.  Once you venture beyond the range of dates for which the model is 
tuned, numerical artifacts in the model will accumulate, making the 
prediction less and less accurate as more remote dates are examined.  You can 
get some more details about this in the README.planetmath file, in the root 
kstars directory, and also in the FAQ chapter of the KStars handbook.

Now, given all that, the good news is that the Moon and Sun subtend large 
angles on the sky.  So, even if the cumulative error in the Moon's position 
was something like 10 arcseconds per century (a number I just made up, but 
probably not too far off), you still have a window of +- 9000 years over 
which (partial) eclipses could be predicted.  That is, if the error 
accumulates at 10 arcsec per century, you need 90 centuries before the error 
reaches 15 arcmin, the angular radius of the Moon.

However, I would not use KStars for your research.  Fred Espanek is the 
world's expert on eclipses, and he has published a table of all eclipses over 
the years -1900 to +4000.  This table represents our best knowledge about 
prehistoric eclipses.  Unfortunately that page does not discuss the errors of 
the predictions, but perhaps you can email him about it.  In any case, you 
can find the table here:

http://sunearth.gsfc.nasa.gov/eclipse/SEcat/SEcatalog.html

Good luck,
Jason

-- 
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KStars: KDE Desktop Planetarium
http://edu.kde.org/kstars