Zague wrote:
My question may call for an obvious answer but I need confirmation
anyway. My planetarium software doesn't go back far enough (-99 999 BC
for Starry Night) and I don't have access to it now. I might have seen
that the sky is already unrecognizable 104,000 years ago.

Would it be safe to say that, except for the Milky Way, the Moon and
planets, the nightsky would have looked totally alien to us because
nearby stars would be in much different positions in the sky?

I see you already have gotten a variety of answers.

Proper motion is the only motion that would distort the appearance of
the night sky. The other motions, like precession, can change what
part of the sky is visible at night, but not what each part looks like.

Proper motions vary over the lot, with Barnard's Star the fastest at
nearly 10 arcseconds per year, but a typical value is more like 100
milliarcseconds (mas) or so. Over a period of 100,000 years, that
translates to a motion of perhaps 3 or 4 degrees--several times the
width of the Full Moon.

A difference of 3 degrees may not seem like a lot, but since motions
vary randomly and largely independently (constellations generally do
not consist of actual physical associations, with Ursa Major and
Scorpius two of the notable exceptions), the stars will not be moving
3 degrees together, but instead wandering in different directions.
I suspect that if you were very familiar with the sky as it is now,
you could perhaps reconstruct them 100,000 years ago (or into the
future), but it wouldn't be very easy.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
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