APOD: Two Million Stars on the Move (2017 Apr 17)

Comments and questions about the APOD on the main view screen.
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APOD: Two Million Stars on the Move (2017 Apr 17)

Postby APOD Robot » Mon Apr 17, 2017 4:10 am

Image Two Million Stars on the Move

Explanation: If you could watch the night sky for one million years -- how would it change? Besides local effects caused by the Earth's spin and the reorientation of the Earth's spin axis, the stars themselves will move. Combining positional data of unprecedented accuracy for two-million stars taken over years by ESA's Earth-orbiting Hipparcos (now defunct) and Gaia satellites, a future extrapolation of star movements was made over millions years. As shown in the featured video, many stars make only small angular adjustments, but some stars -- typically those nearby -- will zip across the sky. Once familiar constellations and asterisms will become unrecognizable as the bright stars that formed them move around. Not shown are many local nebulas that will surely dissipate while new ones will likely form in different places. Perhaps reassuringly, future Earth inhabitants will still be able to recognize the central band of our Milky Way Galaxy.

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Gaia: Two Million Stars on the Move

Postby bystander » Mon Apr 17, 2017 4:12 am

Two Million Stars on the Move
ESA Science & Technology | Gaia | 2017 Apr 12

The changing face of our Galaxy is revealed in a new video from ESA’s Gaia mission. The motion of two million stars is traced 5 million years into the future using data from the Tycho-Gaia Astrometric Solution, one of the products of the first Gaia data release. This provides a preview of the stellar motions that will be revealed in Gaia's future data releases, which will enable scientists to investigate the formation history of our Galaxy. ...

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Re: APOD: Two Million Stars on the Move (2017 Apr 17)

Postby Boomer12k » Mon Apr 17, 2017 6:19 am

Well, fine, but not very helpful... I don't recognize any of the stars in the first place for any comparison, it looks like a SCREEN SAVER... they should NAME some next time...

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Re: APOD: Two Million Stars on the Move (2017 Apr 17)

Postby Case » Mon Apr 17, 2017 7:34 am

APOD Robot wrote:Not shown are many local nebulas that will surely dissipate while new ones will likely form in different places. Perhaps reassuringly, future Earth inhabitants will still be able to recognize the central band of our Milky Way Galaxy.

I would think the dark dust clouds that shape the appearance of the Milky Way Galaxy would also move. Wikipedia says that e.g. the Great Rift is only 300 light years away, so any movement of that would be more apparent than if it were much farther away. Understandably, one can’t plot stars obscured from view, but it would impact the recognisability of the central band.

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Re: APOD: Two Million Stars on the Move (2017 Apr 17)

Postby heehaw » Mon Apr 17, 2017 8:56 am

I agree with the previous comments, but it is still great to have these data. Add music to the video; it is all symbolic!
Also, it reminds me of a great experience I had about 30 years ago: I had been invited (along with about a hundred other astronomers) to NASA Headquarters to be part of the audience for a few prominent astronomers giving talks to the NASA Administrator (who just stood in front of us and listened to them). The talks were on the need for Hubble (which had been turned down by OMB). Anyway, Phil Morrison was one of the speakers, and I'll now ask YOU what Phil asked them: picture, in your mind, the Andromeda Galaxy. OK! did you do it? Phil: you did it wrong!! You saw it in your mind as you would see it in a picture. The problem with that is that you did not adopt an appropriate time frame! Andromeda rotates in about 200 million years! So do it again, this time allowing Andromeda to slowly rotate in your mental picture! Everyone including me dutifully did that. Then came the kicker - Phil said "I bet you are STILL doing it wrong! I'll bet you got a very incorrect picture of what you would see if you could REALLY watch Andromeda with it doing full rotations in a couple of minutes! Because .... you forgot the supernovae! They are going off every 100 years or so! You should have visualized a pinwheel firecracker, not a rotating still photo!"
Phil had a remarkable mind. However, Rainer Weiss said that he had had to fight against Phil to get LIGO going; Phil had been strongly opposed to it; I think he didn't believe in gravitational waves.

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Re: APOD: Two Million Stars on the Move (2017 Apr 17)

Postby geckzilla » Mon Apr 17, 2017 9:36 am

Case wrote:
APOD Robot wrote:Not shown are many local nebulas that will surely dissipate while new ones will likely form in different places. Perhaps reassuringly, future Earth inhabitants will still be able to recognize the central band of our Milky Way Galaxy.

I would think the dark dust clouds that shape the appearance of the Milky Way Galaxy would also move. Wikipedia says that e.g. the Great Rift is only 300 light years away, so any movement of that would be more apparent than if it were much farther away. Understandably, one can’t plot stars obscured from view, but it would impact the recognisability of the central band.

The motion of the dust itself would have to be measured for the video to include that. Here it's just the motion of stars.
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Re: APOD: Two Million Stars on the Move (2017 Apr 17)

Postby BDanielMayfield » Mon Apr 17, 2017 11:16 am

An excellent first approximation of how the view will change over the next million years, but one can always wish for upgrades to make such a simulation even more realistic looking:

    1. Add color. Stars are hardly monochromatic.
    2. Add more contrast. The brightness range of stars vary tremendously, way more than we even can accurately depict, but this sim doesn't show bright stars at all.
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Re: APOD: Two Million Stars on the Move (2017 Apr 17)

Postby rj rl » Mon Apr 17, 2017 12:54 pm

Doesn't seem to take the Sun's movement into consideration. Also the Milky Way's spin, although I'm not sure if we have enough data to model that.

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Re: APOD: Two Million Stars on the Move (2017 Apr 17)

Postby Fred the Cat » Mon Apr 17, 2017 12:55 pm

“As the World Turns” the galaxy emerges. Complexity rules. :thumb_up:
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Re: APOD: Two Million Stars on the Move (2017 Apr 17)

Postby Chris Peterson » Mon Apr 17, 2017 1:32 pm

rj rl wrote:Doesn't seem to take the Sun's movement into consideration. Also the Milky Way's spin, although I'm not sure if we have enough data to model that.

As the Sun takes over 200 million years to make one orbit inside the Milky Way, and it is the individual orbits of stars that define the Milky Way's spin, I wouldn't expect to see much in a mere one million years.
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Re: APOD: Two Million Stars on the Move (2017 Apr 17)

Postby dbooksta » Mon Apr 17, 2017 1:50 pm

Frequently, close stars are seen accelerating into a speedy elliptic arc that decays to near motionlessness, characteristic of a close encounter with a relatively large mass. But I can't see anything that they would obviously be orbiting. Are there a bunch of nearby black holes or something?

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Re: APOD: Two Million Stars on the Move (2017 Apr 17)

Postby neufer » Mon Apr 17, 2017 2:16 pm

dbooksta wrote:
Frequently, close stars are seen accelerating into a speedy elliptic arc that decays to near motionlessness, characteristic of a close encounter with a relatively large mass. But I can't see anything that they would obviously be orbiting. Are there a bunch of nearby black holes or something?

The rapid motion of stars that come close within the next million years
is basically straight line 3D motion projected onto the 2D mapping.
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Re: APOD: Two Million Stars on the Move (2017 Apr 17)

Postby BDanielMayfield » Mon Apr 17, 2017 2:30 pm

neufer wrote:
dbooksta wrote:
Frequently, close stars are seen accelerating into a speedy elliptic arc that decays to near motionlessness, characteristic of a close encounter with a relatively large mass. But I can't see anything that they would obviously be orbiting. Are there a bunch of nearby black holes or something?

The rapid motion of stars that come close within the next million years
is basically straight line 3D motion projected onto the 2D mapping.


A good answer Art. Rest easy dbooksta, no black holes were used in the production of this model.

Would love to see the brightness changes with changing distance to be more pronounced than it is here though.

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Re: APOD: Two Million Stars on the Move (2017 Apr 17)

Postby dbooksta » Mon Apr 17, 2017 2:31 pm

neufer wrote:
dbooksta wrote:
Frequently, close stars are seen accelerating into a speedy elliptic arc that decays to near motionlessness, characteristic of a close encounter with a relatively large mass. But I can't see anything that they would obviously be orbiting. Are there a bunch of nearby black holes or something?

The rapid motion of stars that come close within the next million years
is basically straight line 3D motion projected onto the 2D mapping.


Ah ha: You mean it's the result of distance perspective as they go from near to far.

What I was referring to is something like the star in the top left that at :20 accelerates from near stationary towards the right and by :22 has passed the middle of the map and decelerates to then drift very slowly towards the "horizon." That arc from :20 to :22 looks like an elliptic projection. Or is it something else?

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Re: APOD: Two Million Stars on the Move (2017 Apr 17)

Postby Ann » Mon Apr 17, 2017 2:37 pm

Black and white is the new black for APOD!

Seriously, this kind of APOD could not have been made in color. I like the APOD. It is fascinating, and I look forward to more from Gaia!

As for Milky Way's dust lane, it will certainly be mostly unchanged a million years from now. The Milky Way has a thick dust lane, and a million years is almost nothing in the life of a galaxy - at least if the galaxy in question isn't undergoing a major merger in that time. And ours won't, not in just a million years!

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Re: APOD: Two Million Stars on the Move (2017 Apr 17)

Postby neufer » Mon Apr 17, 2017 2:41 pm

dbooksta wrote:
neufer wrote:
dbooksta wrote:
Frequently, close stars are seen accelerating into a speedy elliptic arc that decays to near motionlessness, characteristic of a close encounter with a relatively large mass. But I can't see anything that they would obviously be orbiting. Are there a bunch of nearby black holes or something?

The rapid motion of stars that come close within the next million years
is basically straight line 3D motion projected onto the 2D mapping.

Ah ha: You mean it's the result of distance perspective as they go from near to far.

What I was referring to is something like the star in the top left that at :20 accelerates from near stationary towards the right and by :22 has passed the middle of the map and decelerates to then drift very slowly towards the "horizon." That arc from :20 to :22 looks like an elliptic projection. Or is it something else?

Rapid distorted motion nears the Mercator mapping poles is related to
the grotesque distortions of Greenland in standard Mercator mappings of the Earth
(or flight paths from Tokyo to Washington, D.C. on same).
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Re: APOD: Two Million Stars on the Move (2017 Apr 17)

Postby dbooksta » Mon Apr 17, 2017 2:51 pm

neufer wrote:Rapid distorted motion nears the Mercator mapping poles is related to
the grotesque distortions of Greenland in standard Mercator mappings of the Earth
(or flight paths from Tokyo to Washington, D.C. on same).


Even if this is a Mercator-like projection, I was thinking that it covers such a narrow band on the vertical axis that I can't see that explaining the example I gave as being a star with a constant velocity as it moves from left to right.

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Re: APOD: Two Million Stars on the Move (2017 Apr 17)

Postby Chris Peterson » Mon Apr 17, 2017 3:20 pm

Ann wrote:Black and white is the new black for APOD!

Seriously, this kind of APOD could not have been made in color.

That's true using the first Gaia dataset release. However, in addition to position Gaia also measures photometric data. Only the G-band data is released in the first dataset, but in the next the red and blue data will be present, as well, meaning that the effective temperatures of the stars will be known, and therefore their colors.
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Re: APOD: Two Million Stars on the Move (2017 Apr 17)

Postby Ann » Mon Apr 17, 2017 3:30 pm

neufer wrote:Rapid distorted motion nears the Mercator mapping poles is related to
the grotesque distortions of Greenland in standard Mercator mappings of the Earth
(or flight paths from Tokyo to Washington, D.C. on same).



Yes, Mercator mappings make Greenland (almost) the same size as Africa, and bigger than South America.

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Re: APOD: Two Million Stars on the Move (2017 Apr 17)

Postby BDanielMayfield » Mon Apr 17, 2017 3:34 pm

Ann wrote:Seriously, this kind of APOD could not have been made in color.


Why not? In addition to recording proper motion changes over time Gaia takes stellar spectra so it can accurately measure motions toward or away from us as well. If you have a star's spectra you also have the star's color.

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Re: APOD: Two Million Stars on the Move (2017 Apr 17)

Postby bystander » Mon Apr 17, 2017 3:42 pm

BDanielMayfield wrote:
Why not? ...

See Chris's answer above.

edit:
ESA wrote:...
On its way to assembling the most detailed 3D map ever made of our Milky Way galaxy, Gaia has pinned down the precise position on the sky and the brightness of 1142 million stars.

As a taster of the richer catalogue to come in the near future, today’s release also features the distances and the motions across the sky for more than two million stars. ...

See a detailed description of the video here.
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Re: APOD: Two Million Stars on the Move (2017 Apr 17)

Postby Steve Dutch » Mon Apr 17, 2017 5:02 pm

Note that the first couple of hundred thousand years have lots of fast-moving stars as nearby stars zip past us and recede. Then they become much less common. No doubt their replacements are out there but GAIA hasn't spotted them yet.

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Re: APOD: Two Million Stars on the Move (2017 Apr 17)

Postby ThePiper » Mon Apr 17, 2017 6:21 pm

heehaw wrote:I agree with the previous comments, but it is still great to have these data. Add music to the video; it is all symbolic!
Also, it reminds me of a great experience I had about 30 years ago...


heehaw - I always appreciate your sense of humor and the experience reports providing insights into the exciting work of scientists. Thank you! :)
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Re: APOD: Two Million Stars on the Move (2017 Apr 17)

Postby geckzilla » Mon Apr 17, 2017 7:51 pm

Ann wrote:Black and white is the new black for APOD!

Seriously, this kind of APOD could not have been made in color. I like the APOD. It is fascinating, and I look forward to more from Gaia!

As for Milky Way's dust lane, it will certainly be mostly unchanged a million years from now. The Milky Way has a thick dust lane, and a million years is almost nothing in the life of a galaxy - at least if the galaxy in question isn't undergoing a major merger in that time. And ours won't, not in just a million years!

Ann

I'm not sure we know enough to say that for certain. Dust is just as dynamic as stars and some parts change a lot while other parts aren't undergoing much change. A million years might be plenty of time to see significant changes especially in areas of star formation. Of course, this whole galaxy view might indeed be too broad to notice much.
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Re: APOD: Two Million Stars on the Move (2017 Apr 17)

Postby neufer » Mon Apr 17, 2017 8:47 pm

https://en.wikipedia.org/wiki/Anaxagoras wrote:
<<Anaxagoras (Ἀναξαγόρας, "lord of the assembly"; c. 510 – c. 428 BC), a Pre-Socratic Greek philosopher born in Clazomenae in Asia Minor, was the first to bring philosophy to Athens. Heavenly bodies, he asserted, were masses of stone torn from the earth and ignited by rapid rotation. Anaxagoras explained that both sun and the stars were fiery stones but that we don't feel the heat of the stars because of their enormous distance from earth. Anaxagoras produced a correct explanation for eclipses and described the sun as larger than the Peloponnese. According to Diogenes Laertius and Plutarch, in later life he was charged with impiety and went into exile in Lampsacus; the charges may have been political, owing to his association with Pericles.

Anaxagoras is referred to and admired by Cyrus Spitama, the hero and narrator of Creation, by Gore Vidal. The book contains this passage, explaining how Anaxagoras became influential:

[According to Anaxagoras] One of the largest things is a hot stone that we call the sun. When Anaxagoras was very young, he predicted that sooner or later a piece of the sun would break off and fall to earth. Twenty years ago, he was proved right. The whole world saw a fragment of the sun fall in a fiery arc through the sky, landing near Aegospotami in Thrace. When the fiery fragment cooled, it proved to be nothing more than a chunk of brown rock. Overnight Anaxagoras was famous. Today his book is read everywhere. You can buy a secondhand copy in the Agora for a drachma.>>
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