>
> Probably a value not very different from yours. But the interesting
> part was the deviation of Guide's delta-T from the real delta-T, not
> from SkyMap's delta-T :-)

Yes, but the delta T values which all these modern programs use *is* based
on historical data - primarily the visibility of ancient solar eclipses.
That gives us a whole series of pretty accurate data points going back to
1500 BC or beyond. That's why I say that although delta T is uncertain for a
couple of thousand years ago, the uncertainty in its value is only a few
minutes.

Regards,

Chris
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Chris Marriott, SkyMap Software, UK (chris@...)
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