NavList:

Peter, you asked:
"Frank, I take it that your site provides data that IS accurate for
analysis of historical sights? Past, present and future? "

Future history - if any...

Yes, the nav tools on my web site are accurate to +/-1 arcsecond for
the period 1750-2050, with the usual uncertainty with respect to
delta-T for future dates. Since the display style most often selected
for almanac data today is degrees, minutes, and tenths of minutes, that
arcsecond either way will show up as a disagreement to the nearest
tenth of a minute when compared with more accurate almanac data in one
out six cases, on average. In other words, an angle of 10d 45' 02.9"
will round to 10d 45.0' while an angle of 10d 45' 03.1" will round to
10d 45.1' giving the appearance of an error of 0.1' when the actual
error is much smaller.

The Solar System almanac data underlying my online navigation tools is
not re-computed from algorithms. It's just the data from the usual JPL
integration, which is believed to be extremely accurate, rounded to the
nearest arcsecond and sampled at time intervals such that no more than
an arsecond error is introduced. The positions of the stars are
calculated based on the algorithms for precession, nutation, proper
motion, etc. in Meeus's Astronomical Algorithms, and the results are
accurate to less than one arcsecond.

-FER


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