On Fri, 10 Apr 2015 23:18:37 -0400, Lord Vath
wrote:

On Fri, 10 Apr 2015 17:12:44 -0600, Chris L Peterson
wrote this crap:


Essentially all planetarium apps calculate precession and use it for
plotting the sky in the past and future. Keep in mind that the values
used for long time scales are approximations, and not very good ones.
Accurate calculations of precession beyond a couple thousand years in
either direction don't exist.

I don't believe you. At the university I went to school at, I was
very familiar with the planetarium. The stars were projected on the
ceiling dome with a globe which had lights attached. The lights were
fixed which could not have provided precession.

I'm not sure why you're discussing planetariums. The discussion is
about planetarium software.

That said, precession doesn't change the pattern of the stars, only
their position with respect to the Earth's poles. Plenty of old-style
star ball planetariums could demonstrate precession.

Perhaps there are newer types which allow for precession, but I
haven't been into a planetarium in 35 years.

Most planetarium projectors these days are digital, and can project
any image. These are controlled by planetarium software similar to the
programs we're discussing here, so in addition to precession, they can
also correct for stellar proper motion, and therefore show how well
known constellations have changed their shapes in the past, and will
do so in the future.