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How far back in time would the Milky Way be recognizable?

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#1 birger

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Posted 22 July 2021 - 01:36 PM

I played around with SkySafari, and investigated the sky 100,000 years ago. Many constellations are completely unrecognizable. The Big Dipper looks very strange, and only Orion bears some resemblance to its modern appearance.

 

The Milky Way texture is however not changed due to program limitations. My question is, how much would the Milky Way have differed? Would famous dark nebulae, such as the Coalsack, be in a different position? Would the spiral arms look different?

 

Screenshot of how the sky probably looked about 100,000 years ago:

stars100000BC.jpg

 

A similar, heavily related question: How far away from Earth would one have to travel to see a noticeably different Milky Way in the sky?



#2 spereira

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Posted 22 July 2021 - 01:48 PM

Moving to Deep Sky Observing.

 

smp



#3 MikiSJ

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Posted 22 July 2021 - 02:44 PM

I am going to guess that 50,000 years ago, early hominids didn't understand the stuff they saw at night - so  50,000 years works for me.

 

But more seriously, if one were to be in a non-Milky Way viewpoint, then they would see a changing Milky Way as it wends itself in a galactic plane rotation that circles around every couple of million years. 

 

So, the CoalSack would not be where it was a million years ago.



#4 stargzr66207

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Posted 23 July 2021 - 12:23 PM

For the purposes of Human history, the Milky Way would not have changed much at all. After all, the Milky Way is our galaxy, which was in existence long before Earth came into being. And, the time that Humans and our predecessors have been around, is but the blink of an eye in the history of the Earth. So for all intents and purposes, you could say that, as long as the time Humans have existed, the Milky Way has been an unchanging element of the night sky.

Ron Abbott



#5 Tony Flanders

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Posted 25 July 2021 - 06:05 AM

This is largely a matter of distance. All of the sky's bright stars are quite close to us -- otherwise they wouldn't appear bright. Orion's stars are among the most distant -- visible because they're extremely young and luminous -- but even they are just 1,500 light-years or thereabouts, making them still well within the same spiral arm as our own Sun. And aside from the "runaway" star Betelgeuse, Orion's shape hasn't changed significantly in the course of human history.

 

All of the major Milky Way features visible to the unaided eye are quite a lot farther, meaning that they appear to move much more slowly from our perspective.


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#6 Redbetter

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Posted 25 July 2021 - 07:39 AM

This is largely a matter of distance. All of the sky's bright stars are quite close to us -- otherwise they wouldn't appear bright. Orion's stars are among the most distant -- visible because they're extremely young and luminous -- but even they are just 1,500 light-years or thereabouts, making them still well within the same spiral arm as our own Sun. And aside from the "runaway" star Betelgeuse, Orion's shape hasn't changed significantly in the course of human history.

 

All of the major Milky Way features visible to the unaided eye are quite a lot farther, meaning that they appear to move much more slowly from our perspective.

That was my thought when I read the title as well.  The Milky Way as we see it from Earth will have changed little, but the constellations and individual star positions and magnitudes will have changed by a lot over tens of thousands of years.  


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#7 MeridianStarGazer

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Posted 25 July 2021 - 09:54 PM

Most of the stars we can see are within 1000 light years from earth, and are very bright, much brighter than the sun. Vega is 25 light years. Acturus 400.

The earth is 25,000 light years away from the center of the milky way and orbits it every 60 million years.



#8 Redbetter

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Posted 26 July 2021 - 01:49 AM

Sources I have read indicate ~220 to 250 million years = 1 orbit of the Sun around the Milky Way or 1 galactic year.


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#9 birger

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Posted 26 July 2021 - 02:29 AM

Thank you all for explaining. I keep forgetting that the Milky Way is made up of stars at a very great distance. Ok, so SkySafari is correct to assume the Milky Way has not changed appearance noticeably since 100,000 BC. In fact, many stars are still in roughly the same position in the sky. Some stars are much brighter, such as Aldebaran and Capella, but others, such as Alpha Centauri, are almost too faint to see with the naked eye because of the increased distance compared to today.



#10 EricSi

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Posted 26 July 2021 - 12:55 PM

Individual features such as the Coal Sack might change, but the overall appearance should be pretty much the same going back to when the Sun was formed.



#11 birger

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Posted Yesterday, 03:46 AM

Individual features such as the Coal Sack might change, but the overall appearance should be pretty much the same going back to when the Sun was formed.

Really? We talk a time period of 4.6 billion years, over which the Milky Way would have rotated more than 20 times around its centre (Sun's orbit). Would that really keep the overall appearance?



#12 Tony Flanders

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Posted Yesterday, 06:40 AM

Really? We talk a time period of 4.6 billion years, over which the Milky Way would have rotated more than 20 times around its centre (Sun's orbit). Would that really keep the overall appearance?

To some extent the answer is "nobody knows." The dynamics of spiral galaxies are still poorly understood. There's still no consensus even on something as fundamental as why spiral arms form at all.

 

But the short answer is that even if the grand plan stays the same, each and every detail changes dramatically within one billion years.


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#13 skysurfer

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Posted Yesterday, 06:57 AM

This is also interesting: https://en.wikipedia...brightest_stars

 

Some stars 'pass by' such as e.g. Epsilon Canis Majoris, which is now still +1.8, but was -4 4 million years ago.


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#14 birger

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Posted Today, 04:36 PM

To some extent the answer is "nobody knows." The dynamics of spiral galaxies are still poorly understood. There's still no consensus even on something as fundamental as why spiral arms form at all.

 

But the short answer is that even if the grand plan stays the same, each and every detail changes dramatically within one billion years.

Interesting! I had no idea we knew so little about galaxy formation and rotation. I hope to live to see more detailed scientific models on spiral galaxies. smile.gif

 

This is also interesting: https://en.wikipedia...brightest_stars

 

Some stars 'pass by' such as e.g. Epsilon Canis Majoris, which is now still +1.8, but was -4 4 million years ago.

Yes, I've seen that link too. Very interesting! I would have liked to see Aldebaran at its peak. Just as bright as Sirius is today, but red! cool.gif I envy those Neanderthals who got to see that.




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