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Thread: Andromeda........

  1. #1 Andromeda........ 
    Forum Professor leohopkins's Avatar
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    Okay, so at inflation and the big bang all of the galaxies (held together by gravity) flew apart, hence the red shift and BB and inflation theory. someting that startles and confuses me though is that the Andromeda galaxy is speeding TOWARDS us. Why ?


    The hand of time rested on the half-hour mark, and all along that old front line of the English there came a whistling and a crying. The men of the first wave climbed up the parapets, in tumult, darkness, and the presence of death, and having done with all pleasant things, advanced across No Man's Land to begin the Battle of the Somme. - Poet John Masefield.

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  3. #2  
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    im gonna guess it is inbetween us and the "center" of the universe. Ill wait to see just how wrong i am


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    WYSIWYG Moderator marnixR's Avatar
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    the andromeda galaxy is part of the "local group"

    galaxies within the local group seem to be gravitationally tied together (as are presumably other galaxies in their own local group), hence are the exception to the rule that all galaxies move away from us
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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  5. #4  
    Forum Professor leohopkins's Avatar
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    So actually, all "local groups" are moving away from each other, individual galaxies are not.
    The hand of time rested on the half-hour mark, and all along that old front line of the English there came a whistling and a crying. The men of the first wave climbed up the parapets, in tumult, darkness, and the presence of death, and having done with all pleasant things, advanced across No Man's Land to begin the Battle of the Somme. - Poet John Masefield.

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    WYSIWYG Moderator marnixR's Avatar
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    that's my understanding of it
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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  7. #6  
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    The universe is expanding. All objects of mass within the universe are still subject to gravity ...a grain of sand and a galaxy. If I throw a ball in the air it is attracted to the Moon but will still be more attracted to the mass of earth (and thus fall to the ground). If I throw an object with enough energy then that object may reach the Moon. It's the same with large objects like stars, local star groups, groups of galaxies, etc. They are all subject to the same forces. The universe expands (space/time) increases but not the masses within that space/time. The masses still impact each other in the same way according to their size distance and other gravitatioal forcces acting upon them.
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    but the stars just sit there and revolve around the sun...gravity is what pulls things down but it is the energy that resists gravity right?
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    Quote Originally Posted by irontony88
    but the stars just sit there and revolve around the sun...gravity is what pulls things down but it is the energy that resists gravity right?
    stars just sit there and revolve around the sun? the sun is a star...

    Gravity pulls things in and energy can resist gravity, but it depends how it is being used.
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  10. #9  
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    All objects want to move in a Straight line in the direction theyre already going. Mass creates gravity which tries to alter the direction of objects nearby toward the centre of the mass. The larger and heavier the object, the more gravity it makes. Gravity is reasonably weak, so an object has to be really really big for gravitational effects to become large enough to effect the direction of nearby objects. Also the further away an object is from something, the weaker the attraction of gravity is.

    Planets go around the Sun because the sun is Very very big. If the earth was the size of a peanut, then the sun would be something like a city block for comparison.

    The moon goes around the Earth because the Earth happens to be far closer. If the moon went around the earth in an orbit the size of your average roundabout, The earth is going around the sun in an orbit about the size of your average US State border.

    Thus the closer you are, the better gravity works.

    Now because objects want to move in a straight line, they resist the application of turning force. you can test this out in a car. Drive around a tight corner with some reasonable speed and you will find your body trying to pull "out of the turn". Not just your body, but any and all objects. In this case the reason you are turning is Friction between your tyres and the ground. The angle of the wheels forces the car to turn, however even it's chassis and body don't want to break their straight line, and you can see this whenever you see a car skid around a corner. The force of the matter fighting against turning causes the car's tyres to loose the grip on the road.

    The earth is doing the same, except in space there is no friction and so you will never actually slow down. The sun is trying to pull the earth "Straight down" into the middle of the sun, but the earth's mass wishes to continue it's current direction in a straight line. One way to think of an orbit is like this:

    The Sun/Earth is trying to pull you straight down toward it's centre. So you fall. The Sun/Earth can only accellerate you using gravity, which is limited by the size and proximity of the Sun/Earth and you will fall to whichever one is strongest, based on both distance and size. The Sun/Earth can only accelerate you at a certain rate, say 9.8m/s/s. (ie accelerating toward Earth at 9.8 metres per second adding 9.8 meters per second to your current velocity every second)

    However you are moving forwards also at a high speed, and by the time that you get to the point where the surface would have been, you have moved so far that it has carried you away from the surface of the object.

    So for the idea about the universe expanding. The expansion of the universe does not trump existing Gravitational Relationships. Things which are massive and close will be attracted to each other, either in a collision relationship, or in an orbit (where the forward velocities are high enough so that the objects fall toward each other at a rate low enough so that their forward velocity carries them out of the way). This never changes, however things which are not gravitationally attracted (either through pure distance, or because there is not enough mass, or both) are free to move about.

    Now everything in our galaxy is close enough to the centre of the galaxy, and unique objects inside the galaxy, outskirts to centre, to be gravitationally bound to the galaxy and either orbit the galaxy COG as a whole, or a specific object inside the galaxy such as other stars etc. Our Sun is out in the arm of the galaxy, nowhere near the centre.

    It's easier to think of things with a centre if they are solid spheres like Earth, so an analogy. Imagine The Galaxy is like Earth. A solid Sphere, with the Centre of mass being, predictably, the centre. The centre of mass isn't the "Cause" of gravity, the entire object is. However it is the acceleration point to which the 'vector' or direction of travel is centred toward as far as gravitational attraction is concerned. You standing on the ground is you being attracted to the mass of Earth itself, but the direction of attraction is to the centre of the planet, not to random points everywhere along the surface of the planet. You can tell this because you still fall "Down" when you are underground. This "Toward Centre" momentum would continue even if you are thousands of miles underground. However if you somehow removed all the dirt and rock and lava surrounding the centre of the earth, the mass of the earth and thus it's Gravity would reduce.

    Our sun is in a portion of our galaxy which is like the Dirt and Lava of the earth. Not the centre, but contributing to the galaxy's mass. The sun itself is attracted to the 'centre' of the galaxy but is of course moving through space at high speed. The Sun is in orbit around the Galaxy. However it also makes up the mass of the galaxy.

    Just like a rock on earth. A rock is on the surface of Earth. it is on the surface because it is being attracted to Earth's Centre by gravity. However it also contributes to the Earths Gravity.

    Now Andromeda is a galaxy like hours. Just like the moon is a pile of rocks like Earth. Andromeda is coming closer to our galaxy because of gravity. All the stars in Andromeda are bound to Andromeda, like the rocks of the moon are all attracted to the moon, however the entire Andromeda galaxy as a whole is attracted by the gravity of our Galaxy, in the same way the moon is attracted to the earth. The stars of Andromeda don't individually become attracted to Milky Way. They Andromeda is closer to the individual stars and thus exerts greater influence, however the entire collective mass of the Andromeda is influenced by the entire collective mass of the Milky Way.

    Another galaxy group like Virgo are too far away to be effected by the gravity of either of these galaxies, and thus ride freely in comparison on the expansion of space-time. The Groups are moving apart because space itself is getting larger. Stretching like the baloon surface being inflated. However the local groups of galaxies are all locked together in Gravity and cannot change size. like coins stuck to the balloon.
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  11. #10  
    Forum Professor leohopkins's Avatar
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    Thanks. Makes sense.
    The hand of time rested on the half-hour mark, and all along that old front line of the English there came a whistling and a crying. The men of the first wave climbed up the parapets, in tumult, darkness, and the presence of death, and having done with all pleasant things, advanced across No Man's Land to begin the Battle of the Somme. - Poet John Masefield.

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