The StellarMate Plus Manual
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KStars is pretty accurate, but it is not (yet) as precise as it can possibly be.
The problem with high-precision calculations is that you start having to deal
with a large number of complicating factors. If you are not a professional
astronomer, you will probably never have a problem with its accuracy or
precision.
Here is a list of some of the complicating factors which limit the program's
precision:
· Planet positions are only accurate for dates within 4000 years or so of
the current epoch. The planet positions are predicted using a Fourier-
like analysis of their orbits, as observed over the past few centuries. We
learnt in school that planets follow simple elliptical orbits around the
Sun, but this is not strictly true. It would be true only if there was only
one planet in the Solar system, and if the Sun and the planet were both
point masses. As it is, the planets are constantly tugging on each other,
perturbing the orbits slightly, and tidal effects also induce precessional
wobbling. In fact, recent analysis suggests that the planets' orbits may
not even be stable in the long term (i.e., millions or billions of years). As
a rule of thumb, you can expect the position of a planet to be accurate
to a few arcseconds between the dates -2000 and 6000.
Pluto is the exception to this; its position is perhaps ten times less precise
than the positions of the other planets. Still, for dates near the present epoch,
its position can be trusted to about an arcsecond.
The moon's position is the most difficult to predict to high precision. This is
because its motion is quite perturbed by the Earth. Also, since it is so nearby,
even minute effects that would be undetectable in more distant bodies are
easily apparent in the moon.
The objects with the worst long-term precision in the program are the comets
and asteroids. We use a very simplistic orbital model for the minor planets
that does not include third-body perturbations. Therefore, their positions can
only be trusted for dates near the present epoch. Even for the present epoch,
one can expect positional errors among the minor planets of order 10
arcseconds or more.
11. Why do I have to download an improved NGC/IC catalog and Messier object
images? Why not just include them as part of the KStars distribution?
The author of the downloadable NGC/IC catalog has released it with the
restriction that it may not be used commercially. For most KStars users, this is
not a problem. However, it is technically against the KStars license (the GPL)
to restrict usage in this way. We removed the Messier object images from the
standard distribution for two reasons: to simply reduce the size of KStars,
and also because of similar licensing concerns with a couple of the images.
The inline images are significantly compressed to a very low quality from
their original form, so I doubt there is a real copyright concern, but I did
obtain explicit permission from the images' authors to use the few images for
which there was any question about it (see README.images). Still, just to be
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