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Thread: Rotation of the Milkyway

  1. #1 Rotation of the Milkyway 
    Forum Sophomore Estheria Quintessimo's Avatar
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    I was thinking about the rotation of the Galaxy for a story I am working on and I looked something up about it.

    I found this article:
    The Milky Way’s Rotation

    ... and had some questions.

    In the article it says:
    Viewed from “above” – what would be North on Earth – the Milky Way spins in the counter-clockwise direction. Of course, if you were to view it from the other side, it would spin clockwise.
    They provided an image. This one:


    So my questions are:
    If our galaxy spins counter clockwise 'seen' from the North... I can then assume this image provides the south view?
    ... because if this is the south view, then why are the spriral arms te wrong way?

    In the article it also says this:
    ...the entire disk of stars, gas and dust is rotating at approximately 270 kilometers per second (168 miles/second), which translates to 970,000 kilometers/hr
    ...and they conclude the earth will take 225 million years to go around. The galaxy spins at approx 0.1% of lightspeed.

    I was wondering about the 'throw a tennisbal of the train' principle. Now on earth the airdrag will finally slow a tennisbal down. But in space you will have not much resistance.
    So then I started to wonder, what would happen if you leave our galaxy either via the north and south. Yes, less drag in space, but you will still have some drag.
    Seeing the vast distances we are talking about here, then at some point it will still be more advantageous to leave the galaxy either via the north or south if you wanted to travel to the other side, to reduce the time of your travel.
    the drag you will encounter in space will slow you down more as you fly out either north or south, while the galaxy 'disc' keeps spinning below you.

    I think my principle might work,... because when you fly out north or south out of our galaxy, you will become less under the influeance of the rotation of the galaxy,... because you will also be less under the influeance of the darkmatter which is part responsible for its shape.

    Or will it simply not matter, as the vehicle you are travelling in will still be under the influeance of the relative rotation of the galaxy? Nullifying what I am thinking about, so traveling in a straight line would still be faster?

    **Clearification: I am talking about assumed 'conventional' propulsion techniques and vehicles.


    Last edited by Estheria Quintessimo; October 17th, 2013 at 06:08 AM. Reason: correction 28.000 to 225 million
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  3. #2  
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    Quote Originally Posted by Estheria Quintessimo View Post
    So my questions are:
    If our galaxy spins counter clockwise 'seen' from the North... I can then assume this image provides the south view?
    ... because if this is the south view, then why are the spriral arms te wrong way?
    I think this is a north view. The arms are not created by the sort of "drag" effect you are imagining. They are density waves.

    I'm afarid I don't have much idea about your other questions. Although I doubt drag from the interstellar medium is significant. And there would be none from dark matter.


    Without wishing to overstate my case, everything in the observable universe definitely has its origins in Northamptonshire -- Alan Moore
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    Universal Mind John Galt's Avatar
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    Quote Originally Posted by Estheria Quintessimo View Post
    ...and they conclude the earth will take 28.000 years to go around. The galaxy spins at approx 0.1% of lightspeed.
    They do not state that it would take 28,000 years to go around. They very clearly state, correctly, that it would take 225 million years - four orders of magnitude longer. We are approximately 28,000 light years from the galactic centre. Please remember that a light year is a measure of distance and not of time.
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  5. #4  
    Forum Sophomore Estheria Quintessimo's Avatar
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    Me adding the point of the darkmatter was not intented for the drag question,... but more so with escaping the gravitational effect of the galaxy disc.

    Is not the current working theory that the shape of galaxies is determined by the ammount of darkmatter?
    I am assuming that... escaping the gravitational effect of the rotating galaxy disc, you may be able to take advantage of the rotational spin of the galaxy whilst trying to travel to the other side. As you are escaping the gravitational pull of the galaxy you may be able to travel faster as the speed of galaxy spinning below you will be adding to your (relative) travel speed.

    It may be a small advantage, as the disc only rotates at 0.1% of lightspeed,... but seeing the vast distances I am talking about, the effect may still be significant, as it may still shave years of the total ammount needed to travel.
    That was my idea about that.

    But it will depend on the gravitation-field (for lack of a better word) of our galaxy. I am assuming it is also disc shaped and not spherical.

    So the assumed drag from dust and whatever more.... I see seperate from the effect gravitational pull of the galaxy will have.

    I also added 'convential'... because I am basically talking about a vehicle that can only travel at sub light speed, and not even near lightspeed.
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  6. #5  
    Forum Sophomore Estheria Quintessimo's Avatar
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    Quote Originally Posted by John Galt View Post
    Quote Originally Posted by Estheria Quintessimo View Post
    ...and they conclude the earth will take 28.000 years to go around. The galaxy spins at approx 0.1% of lightspeed.
    They do not state that it would take 28,000 years to go around. They very clearly state, correctly, that it would take 225 million years - four orders of magnitude longer. We are approximately 28,000 light years from the galactic centre. Please remember that a light year is a measure of distance and not of time.
    Ah yes, you are correct. I quoted wrong there.

    -Corrected
    Last edited by Estheria Quintessimo; October 17th, 2013 at 06:09 AM.
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  7. #6  
    Brassica oleracea Strange's Avatar
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    Quote Originally Posted by Estheria Quintessimo View Post
    Is not the current working theory that the shape of galaxies is determined by the ammount of darkmatter?
    Not my area of expertise. I think it is a significant factor, but I'm not sure it is "determined" by it.
    Without wishing to overstate my case, everything in the observable universe definitely has its origins in Northamptonshire -- Alan Moore
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    Quote Originally Posted by Estheria Quintessimo View Post
    If our galaxy spins counter clockwise 'seen' from the North... I can then assume this image provides the south view?
    Edit: Never mind. My mistake
    This one's going counterclockwise.
    Last edited by Harold14370; October 17th, 2013 at 07:33 AM.
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  9. #8  
    Moderator Moderator Janus's Avatar
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    Quote Originally Posted by Estheria Quintessimo View Post
    I was thinking about the rotation of the Galaxy for a story I am working on and I looked something up about it.


    the drag you will encounter in space will slow you down more as you fly out either north or south, while the galaxy 'disc' keeps spinning below you.

    I think my principle might work,... because when you fly out north or south out of our galaxy, you will become less under the influeance of the rotation of the galaxy,... because you will also be less under the influeance of the darkmatter which is part responsible for its shape.
    I'm not sure what this "influence" is that you think the rotation of the Galaxy has. What happens is that you just keep moving in the same direction and speed as you were with an new North or South component added. IOW, you pretty much stay just North or South of the Sun. (I say pretty much because the extra North or South component that you added will slightly alter the period of your orbit of the Galaxy.

    Also, going North or South of the disk wouldn't change the gravitational influence of the dark matter on you. Dark matter exists in a larger spherical shape in which the disk of the galaxy is imbedded. Addtionally, the shape of the galaxy is not due in any large degree to dark matter. This is more controlled by how the visible matter interacts and its angular momentum (Only a small fraction of the Dark Matter is in the disk proper.). Where Dark Matter has an influence is in the rotation curve of the galaxy. (How fast stars orbit the center at varying distances.)
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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  10. #9  
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    Quote Originally Posted by Janus View Post
    ... Dark matter exists in a larger spherical shape in which the disk of the galaxy is imbedded. Addtionally, the shape of the galaxy is not due in any large degree to dark matter. This is more controlled by how the visible matter interacts and its angular momentum (Only a small fraction of the Dark Matter is in the disk proper.). Where Dark Matter has an influence is in the rotation curve of the galaxy. (How fast stars orbit the center at varying distances.)
    As the galaxy moves through space, one would expect a change in the "sphere" of dark matter
    less extended beyond the galaxy in the direction of galactic motion?
    or
    is the dark matter pulling the galaxy through the surrounding space, which would indicate that the leading area of dark matter would be more extended?

    thoughts?
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  11. #10  
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    Below is a picture of how our solar system orbits around the galactic center. As you can see it has an up and down movement as it moves in orbit around the galactic center. So at the peaks and valleys there will be many thousands of years when we are outside of the galactic disk. In some theories it is suggested that these cycles may be partially responsible for our climate changes.



    There is also a theory that as our galaxy moves through interstellar space it creates a bow shock wave and that our solar system actually moves into this shock wave as we peak outside the galactic disk.

    Out-of-This-World Hypothesis: Cosmic Forces Control Life on Earth | Space.com
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  12. #11  
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    time
    periodicity?
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  13. #12  
    AI's Have More Fun Bad Robot's Avatar
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    Here's another galactic orbit picture. Our solar system would be in a yellow line orbit.

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  14. #13  
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    Quote Originally Posted by Bad Robot View Post
    Below is a picture of how our solar system orbits around the galactic center. As you can see it has an up and down movement as it moves in orbit around the galactic center. So at the peaks and valleys there will be many thousands of years when we are outside of the galactic disk. In some theories it is suggested that these cycles may be partially responsible for our climate changes.


    This is wrong. While the Sun does have a North-South motion in its orbit in the galaxy, it never gets more than ~200 light years from the galactic equator in this motion. Since the galactic disc in the Sun's region is ~1000 light years thick, the Sun always remains well within the galactic disc. The images shown wildly exaggerate this oscillation( The last one also gets the number of oscillations per orbit wrong, there are only ~4).
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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  15. #14  
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    Quote Originally Posted by Janus View Post
    Quote Originally Posted by Bad Robot View Post
    Below is a picture of how our solar system orbits around the galactic center. As you can see it has an up and down movement as it moves in orbit around the galactic center. So at the peaks and valleys there will be many thousands of years when we are outside of the galactic disk. In some theories it is suggested that these cycles may be partially responsible for our climate changes.


    This is wrong. While the Sun does have a North-South motion in its orbit in the galaxy, it never gets more than ~200 light years from the galactic equator in this motion. Since the galactic disc in the Sun's region is ~1000 light years thick, the Sun always remains well within the galactic disc. The images shown wildly exaggerate this oscillation( The last one also gets the number of oscillations per orbit wrong, there are only ~4).
    I wasn't much of a fan for this theory, after all how much of a bow shock wave could there possibly be in open interstellar space? But I haven't seen the information you just provided, so I was posting what I did find, hoping someone would have a better explanation of what's really happening. It did seem like those oscillations were a bit extreme.
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  16. #15  
    Forum Sophomore Estheria Quintessimo's Avatar
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    Quote Originally Posted by Janus View Post
    Quote Originally Posted by Estheria Quintessimo View Post
    I was thinking about the rotation of the Galaxy for a story I am working on and I looked something up about it.


    the drag you will encounter in space will slow you down more as you fly out either north or south, while the galaxy 'disc' keeps spinning below you.

    I think my principle might work,... because when you fly out north or south out of our galaxy, you will become less under the influeance of the rotation of the galaxy,... because you will also be less under the influeance of the darkmatter which is part responsible for its shape.
    I'm not sure what this "influence" is that you think the rotation of the Galaxy has. What happens is that you just keep moving in the same direction and speed as you were with an new North or South component added. IOW, you pretty much stay just North or South of the Sun. (I say pretty much because the extra North or South component that you added will slightly alter the period of your orbit of the Galaxy.

    Also, going North or South of the disk wouldn't change the gravitational influence of the dark matter on you. Dark matter exists in a larger spherical shape in which the disk of the galaxy is imbedded. Addtionally, the shape of the galaxy is not due in any large degree to dark matter. This is more controlled by how the visible matter interacts and its angular momentum (Only a small fraction of the Dark Matter is in the disk proper.). Where Dark Matter has an influence is in the rotation curve of the galaxy. (How fast stars orbit the center at varying distances.)
    I think you misunderstand...

    I was not talking about leaving the gravitational effect of our sun... I was talking about leaving the gravitational pull of our galaxy. My conventional traveller has been traveling along time already... its goal is (kinda) to reach the other side of our Milkyway using a sub light propulsion system (whatever it is, is not important for this hypothesis, nor how long he has already been or will be travelling)

    As our Galaxy (the Milkyway) is basically disc shaped,... am I save to assume the gravitational-field of our Galaxy looks like this too?
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  17. #16  
    Forum Sophomore Estheria Quintessimo's Avatar
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    Quote Originally Posted by Bad Robot View Post
    Below is a picture of how our solar system orbits around the galactic center. As you can see it has an up and down movement as it moves in orbit around the galactic center. So at the peaks and valleys there will be many thousands of years when we are outside of the galactic disk. In some theories it is suggested that these cycles may be partially responsible for our climate changes.



    There is also a theory that as our galaxy moves through interstellar space it creates a bow shock wave and that our solar system actually moves into this shock wave as we peak outside the galactic disk.

    Out-of-This-World Hypothesis: Cosmic Forces Control Life on Earth | Space.com
    Interresting...
    You are saying... besides the sun and earth and the rest of our personal solar system,... rotating around the Milkyway Galactic Centre,... the Earth also moves Towards the North and South, relative of our Milkyway Galactic Centre?
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  18. #17  
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    Quote Originally Posted by Estheria Quintessimo View Post
    I think you misunderstand...

    I was not talking about leaving the gravitational effect of our sun... I was talking about leaving the gravitational pull of our galaxy. My conventional traveler has been traveling along time already... its goal is (kinda) to reach the other side of our Milkyway using a sub light propulsion system (whatever it is, is not important for this hypothesis, nor how long he has already been or will be traveling)

    As our Galaxy (the Milkyway) is basically disc shaped,... am I save to assume the gravitational-field of our Galaxy looks like this too?
    If you look at the list of the Milkyway's satellite galaxies and the distances they are away and still gravitationally bound to the Milkyway, you might realize that the distance you are talking about is pretty negligible and most likely would not cause the effect you were suggesting.

    List of Milky Way's satellite galaxies - Wikipedia, the free encyclopedia
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  19. #18  
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    Quote Originally Posted by Estheria Quintessimo View Post
    Quote Originally Posted by Bad Robot View Post
    Below is a picture of how our solar system orbits around the galactic center. As you can see it has an up and down movement as it moves in orbit around the galactic center. So at the peaks and valleys there will be many thousands of years when we are outside of the galactic disk. In some theories it is suggested that these cycles may be partially responsible for our climate changes.



    There is also a theory that as our galaxy moves through interstellar space it creates a bow shock wave and that our solar system actually moves into this shock wave as we peak outside the galactic disk.

    Out-of-This-World Hypothesis: Cosmic Forces Control Life on Earth | Space.com
    Interesting...
    You are saying... besides the sun and earth and the rest of our personal solar system,... rotating around the Milkyway Galactic Centre,... the Earth also moves Towards the North and South, relative of our Milkyway Galactic Centre?
    Yes, at least that's what's been posted in a lot of articles. The one article I read suggest that our solar system only enters the galactic bow shock wave on the north upswing. So I can assume that our galaxy is moving at a slight angle to the galactic plain which would allow this to happen. Still I have to wonder what kind of bow wave might be formed in the very near vacuum of interstellar space.
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  20. #19  
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    Quote Originally Posted by Estheria Quintessimo View Post
    Quote Originally Posted by Janus View Post
    Quote Originally Posted by Estheria Quintessimo View Post
    I was thinking about the rotation of the Galaxy for a story I am working on and I looked something up about it.


    the drag you will encounter in space will slow you down more as you fly out either north or south, while the galaxy 'disc' keeps spinning below you.

    I think my principle might work,... because when you fly out north or south out of our galaxy, you will become less under the influeance of the rotation of the galaxy,... because you will also be less under the influeance of the darkmatter which is part responsible for its shape.
    I'm not sure what this "influence" is that you think the rotation of the Galaxy has. What happens is that you just keep moving in the same direction and speed as you were with an new North or South component added. IOW, you pretty much stay just North or South of the Sun. (I say pretty much because the extra North or South component that you added will slightly alter the period of your orbit of the Galaxy.

    Also, going North or South of the disk wouldn't change the gravitational influence of the dark matter on you. Dark matter exists in a larger spherical shape in which the disk of the galaxy is imbedded. Addtionally, the shape of the galaxy is not due in any large degree to dark matter. This is more controlled by how the visible matter interacts and its angular momentum (Only a small fraction of the Dark Matter is in the disk proper.). Where Dark Matter has an influence is in the rotation curve of the galaxy. (How fast stars orbit the center at varying distances.)
    I think you misunderstand...

    I was not talking about leaving the gravitational effect of our sun...
    Neither was I.
    I was talking about leaving the gravitational pull of our galaxy.
    You can't. The best you could do is travel so far away from it that its gravitational pull on you was insignificant. But to to so, you would have travel many times the width of the Galaxy away. Just traveling North of the disk won't do this. All this will do is put you is a different orbit around the galaxy's center.

    As our Galaxy (the Milkyway) is basically disc shaped,... am I save to assume the gravitational-field of our Galaxy looks like this too?
    No.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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  21. #20  
    Forum Sophomore Estheria Quintessimo's Avatar
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    Quote Originally Posted by Janus View Post
    Quote Originally Posted by Estheria Quintessimo View Post
    Quote Originally Posted by Janus View Post
    Quote Originally Posted by Estheria Quintessimo View Post
    I was thinking about the rotation of the Galaxy for a story I am working on and I looked something up about it.


    the drag you will encounter in space will slow you down more as you fly out either north or south, while the galaxy 'disc' keeps spinning below you.

    I think my principle might work,... because when you fly out north or south out of our galaxy, you will become less under the influeance of the rotation of the galaxy,... because you will also be less under the influeance of the darkmatter which is part responsible for its shape.
    I'm not sure what this "influence" is that you think the rotation of the Galaxy has. What happens is that you just keep moving in the same direction and speed as you were with an new North or South component added. IOW, you pretty much stay just North or South of the Sun. (I say pretty much because the extra North or South component that you added will slightly alter the period of your orbit of the Galaxy.

    Also, going North or South of the disk wouldn't change the gravitational influence of the dark matter on you. Dark matter exists in a larger spherical shape in which the disk of the galaxy is imbedded. Addtionally, the shape of the galaxy is not due in any large degree to dark matter. This is more controlled by how the visible matter interacts and its angular momentum (Only a small fraction of the Dark Matter is in the disk proper.). Where Dark Matter has an influence is in the rotation curve of the galaxy. (How fast stars orbit the center at varying distances.)
    I think you misunderstand...

    I was not talking about leaving the gravitational effect of our sun...
    Neither was I.
    I was talking about leaving the gravitational pull of our galaxy.
    You can't. The best you could do is travel so far away from it that its gravitational pull on you was insignificant. But to to so, you would have travel many times the width of the Galaxy away. Just traveling North of the disk won't do this. All this will do is put you is a different orbit around the galaxy's center.

    As our Galaxy (the Milkyway) is basically disc shaped,... am I save to assume the gravitational-field of our Galaxy looks like this too?
    No.
    okay,.. so now even as our galaxy is disc shaped,.. the gravitational pull is still spherical. Thanks for the info, that helps me out a bit.

    So my travelling object will not have have any advantegeous effect moving either north or south of the Milkyway Galaxydisc in an attempt to shorten the travel towards the other end. Assuming the ball being thrown of the train effect, he would be a ball thrown but never able to escape the effect of the moving train. His best attempt to reach the other side of the Milkyway Galaxy,.. would still be simply,... traveling straight through it all.
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