originally posted by: tikbalang
a reply to: AttitudeProblem
Im trying to go past the 100.000BC and AD mark, do you know if its plausible?
I don't think it is.
The extent to which Stellarium plots the motions of stars over a long period of time is limited. It uses the current measurements of
(the apparent angular motion of a star across the sky with respect to more
distant stars) to extrapolate the motion of stars across the sky.
For example, Arcturus has a proper motion of 2.281 arcsec/year. That means in the last 2,000 years its plotted position in the constellation Boötis
has changed by almost 1.27° - two and a half times the angular diameter of the Moon as seen from Earth. That's a lot, and this is reasonably
accurately plotted in Stellarium.
The problem is that stellar motions relative to the Sun are a 3D problem. In addition to the lateral movement that we call Proper Motion, each star
is either moving closer or further away from our Sun. As stars get closer, and pass us, the lateral motion increases to a maximum, then decreases as
they go by and move away. Meanwhile, the rate at which they are approaching (the radial velocity) decreases until it reaches zero at closest
approach, then the rate at which they recede increases (you can see all this as you drive past a row of telephone poles - as you approach, the lateral
movement rate increases until the flash past, and then slows down as they recede in the distance behind you).
Stellarium does not model the change in rate of proper motion; nor does it track changes caused by radial velocity. Arcturus is already receding from
us at 5 kilometers per second. Thus, as time goes on its Proper Motion will decrease. Currently, Stellarium shows Arcturus as a 0.15-magnitude star
36.71 light years away. If you advance its clock 20,000 into the future, it will show that Arcturus' position has changed by ~12.7° (2.281
arcsec/year times 20,000), but it will still be listed and displayed as a 0.15-magnitude star 36.71 light years away. In reality, it will be further
away and fainter, and will not moved as far across the sky from its plotted position.
That said, allow me to point out that Stellarium maps the position of the planets and their moons, and most asteroids & comets with exquisite accuracy
within its +/- 100,000 year time-frame. This is because, instead of extrapolating from a single variable like it does with stellar proper motion, it
calculates each planet's position based on its orbital elements
The only drawback is that it does not track gravitational interactions from close-approaches. This means that if, in Stellarium, you have an asteroid
zip past the Earth a few thousand miles away, it will not accurately predict its post-encounter positions because the program has not recalculated the
asteroid's new orbit.
I think Celestia
does calculate orbital interactions, but I have found it more difficult to use. It is not as
intuitive as Stellarium.
The upshot is that, within the time-frame +/- 10,000 years from the present, Stellarium is quite adequate at plotting the positions of stars.
However, the further you get from the here-and-now, the less-accurate its star maps will be. Its plotting of planets and moons is excellent.
Hope this helps.