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#1
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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 |
#2
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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
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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
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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
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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
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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
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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
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This is quite clear for me now.
Thanks a lot to everyone. |
#9
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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! ---------- Remove 'Z' to reply by email. |
#10
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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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