Warp  wrote in message <45c59d2b@news.povray.org>:
>   Besides that, if it doesn't take into account the slowdown of the
> Earth, it will err by some seconds when speaking about thousands of
> years.

AFAIK, the best available model for the rotation of Earth is (or was)
SMART97, which once was freely downloadable on the FTP site of the Bureau
des Longitudes, and which, fortunately, I still have on a very old backup
CD.

The paragraph about precision is:

# The accuracy of SMART97 has been determined by comparing the analytical 
# solutions of the three Euler angles with a numerical integration computed
# using DE403/LE403. Over 20000 days, between 1968 and 2023, the differences
# are smaller than 2.20 microarcseconds for psi, 0.65 microarcsecond for
# omega, and 2.10 microarcseconds for phi. From the three Euler angles and
# the variations of the ecliptic given by VSOP87, the quantities p, epsilon,
# chi and the sidereal time are computed at the same level of precision.

I can not recall where I found this info, but I seem to recall something
about an error of several degrees on the position of an eclipse during the
Roman Empire.

I believe there is little hope to have accurate data about the position of
the Earth beyond a couple of centuries.

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