You can actually go well beyond years 99999 or -99999. The
accuracy for solar system objects becomes absolutely terrible
for such dates; go far enough into the past and future, and
you'll see the earth passing through the sun once a year, and
the earth's polar axis tumbling end over end, and so on. A
lot of the algorithms were intended for good accuracy over a
period of a few millennia, but not for accuracy over hundreds
of thousands of years.
The star positions, though, ought to be pretty good. If
you click on a star, then on More Info, you'll see the expected
positional accuracy for that date. Of course, that accuracy
will be terrible compared to "present-day" accuracy, but it
will show you that the general shapes of constellations are
well defined, even for very distant times.
> Hello all,
> With guide 9.0 you can now select the year 99999. Is this new?
> I had not noticed this before. The constellations look strange
> in that year (except Orion!?). How accurate is the data?
> Kind regards,