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100 million years ago



 
 
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  #1  
Old December 14th 04, 02:38 PM
Zague
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Default 100 million years ago

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?

Is there any big feature that would be noticeable then that I'm
missing.

Is there a place on the web where simulations, as imprecise as they can
turn going that far in time, can be run just to give me an impression
of what it could have been.

Thanks!

Zague

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  #2  
Old December 14th 04, 03:12 PM
Bob Schmall
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"Zague" wrote in message
oups.com...
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?


Given the 13,000 year cycle of the Earth's polar axis movement, and that
104,000 is an exact multiple of same, the sky would have looked surprisingly
similar then and now. The rotational axis of the Earth would be pointed at
almost exactly the same place in the sky, so a few stars might be in
slightly different positions due to proper motion, but the sky overall would
be about the same.


  #3  
Old December 14th 04, 03:23 PM
Zague
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Thanks Bob. I didn't know that. Can I assume then that proper motion,
even over a 100 million years period, won't make for a different
looking sky ?

Would today's constellation be recognizalbe in some "proto" state ?
Thanks again!

  #4  
Old December 14th 04, 03:24 PM
Chris L Peterson
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On 14 Dec 2004 06:38:27 -0800, "Zague" wrote:

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?


Yes, the sky would have been completely different. Some familiar objects hadn't
even formed yet, and proper motion and the rotation of the galaxy would have
radically altered the constellations.


Is there any big feature that would be noticeable then that I'm
missing.


I don't think so. Naked-eye galaxies like M31, LMC, etc would still have been
visible, but not locatable with respect to any modern star positions.


Is there a place on the web where simulations, as imprecise as they can
turn going that far in time, can be run just to give me an impression
of what it could have been.


I doubt it. The proper motions of most stars isn't that accurately known, and
over this period the position of even very slow stars will change significantly.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
  #5  
Old December 14th 04, 03:40 PM
Sam Wormley
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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.


Just the Big Dipper radically changes +/- 100,000 years.
http://www.google.com/search?q=big+dipper+100000+years

  #6  
Old December 14th 04, 04:03 PM
Brian Tung
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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/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt
  #7  
Old December 14th 04, 04:26 PM
Chris L Peterson
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On Tue, 14 Dec 2004 15:24:51 GMT, Chris L Peterson
wrote:

Yes, the sky would have been completely different. Some familiar objects hadn't
even formed yet, and proper motion and the rotation of the galaxy would have
radically altered the constellations...


Just to be clear here... I'm talking about the sky 100 million years ago (as
given in your subject header) and not about 104,000 years ago (as given in your
message).

104,000 years is certainly enough to distort many of the constellations, but not
always beyond recognition- the sky would be odd, but not totally unfamiliar. 100
million years would produce a totally alien sky.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
  #8  
Old December 14th 04, 04:53 PM
Zague
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This is quite clear for me now.

Thanks a lot to everyone.

  #9  
Old December 14th 04, 06:46 PM
Paul Winalski
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It depends on the particular stars. Some stars with a rather large
proper motion (e.g., Alpha Centauri, Arcturus) might be quite far
away from where they are now. The Ursa Major moving group has large
enough proper motion that the Big Dipper would look very different
100 million years ago than it does now.

Then there are some very young stars that might not even have
existed 100 million years ago. Rigel, for instance. There might
well be no Pleiades in Taurus, and I suspect Orion might look
very different.

-Paul W.


On 14 Dec 2004 07:23:50 -0800, "Zague" wrote:

Thanks Bob. I didn't know that. Can I assume then that proper motion,
even over a 100 million years period, won't make for a different
looking sky ?

Would today's constellation be recognizalbe in some "proto" state ?
Thanks again!


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  #10  
Old December 14th 04, 07:06 PM
Brian Tung
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Paul Winalski wrote:
It depends on the particular stars. Some stars with a rather large
proper motion (e.g., Alpha Centauri, Arcturus) might be quite far
away from where they are now. The Ursa Major moving group has large
enough proper motion that the Big Dipper would look very different
100 million years ago than it does now.

Then there are some very young stars that might not even have
existed 100 million years ago. Rigel, for instance. There might
well be no Pleiades in Taurus, and I suspect Orion might look
very different.


A hundred million years ago, the sky would have been totally
unrecognizable. None of the stars you see today would be where they
are now. They could be halfway across the sky, or totally invisible,
or they might not even exist. (That's particularly possible with
the brightest stars.)

Just a million years would probably be enough to make the sky just
about impossible to recognize, without specialized software.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt
 




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