Why are all galaxies (and solar systems) in a flat plane (instead of a fully random, multi-plane)?
477513
When an object rotates, it has centrifugal force that pushes on its sides, flattening the disk. True, Pluto, Santa (2003 El61), Quouar, Sedna, Buffy, and most kuiper belt objects are not in orbit along the plane of the ecliptic (the usual plane of the orbits), their odd orbits are usually blamed on gravitational influence from Neptune, or a passing star. Comets are also usually not in the plane of the ecliptic. As of this date, I believe, there are no objects in orbit 90 degrees to the plane of the ecliptic.\n\nGalaxies are not related to each other (usually, though they can collide). As I understand it, (and I could be wrong), the shrinking of the galactic disk invokes angular momentum, causing the disk to rotate. And much like protostellar disks, flatten out. Stars form in this gas, causing galaxies. Elliptical galaxies have no plane, and are probably what you would describe as 'multiplane'. Their stars orbit anywhere, and everywhere, around the center.
171073
Rephrase your question sweety, the Milky Way & the Galaxy are the same, but there are other galaxies than ours. then... different than what? are you smoking something?
820102
Well, we know that the galaxy is rotating, if for no other reason than by analogy with other galaxies we see in the universe which we can see rotating.  Moreover, we more or less know the basic shape of the galaxy, which is a rotating disk of stars with a central ball shaped bulge of stars (which also rotates, but the important thing here is the disk).  Additionally we can infer from observations that whatever the center of the galaxy is, we're not it.  :)\n\nUsing the doppler shifts of light, we can tell how fast other stars or clouds of dust in the galaxy are moving with respect to us (but only in the sense that this would be the speed if the star/dust was moving directly towards or away from us).  So, you measure the speed of things around the disk of the galaxy, and there will be four directions in which the speed you measure will be zero.  The final thing we do is look to see which direction has more "stuff".  The direction with more stars and dust (and the central bulge too) is the one which is the center of the galaxy.\n\nNow, if you're wondering why you just wouldn't look for the central bulge or the direction with more stars and dust, well, this will give you the general direction of the galactic center, but it's not very precise.  It's the astronomical equivalent of saying, "It's over that-away".  To get something more precise and exact, you need to do something else, which could be what I was saying above.  Above you would get four pretty precise and exact directions separated by 90 degrees on the sky, and all that's left is to tell which one is towards the center of the galaxy, which is when you fall back on the obvious method as the way to pick between the four more precise answers.  Basically, if you had a big compass engraved on a stone on the ground without any directions marked, having someone tell you that "North is that-away" gesturing in some direction will tell you which of the directions on the compass is north.\n\nOne interesting thing to note is that today our telescopes have improved to the point where we can take pictures of the center of the galaxy and see stars moving around it very quickly.  If we didn't know where the center of the galaxy was and had those pictures we could make a pretty good guess and say that that's where the center of the galaxy is.
16222
The main reason is dust in space that absorbs the light.  For instance, we are in a great big spiral galaxy.  Generally, if you look at a spiral galaxy, you see an immense, bright core.  So why don't we see such a core?  It's because of the dust.  The core, if visible, should be right around the constellation of Sagitarius.  But since there's so much dust in the plane of the galaxy, we can't see it in the invisible spectrum.  Astronomers have managed to infer the direction of the center of the galaxy by looking for a type of light (21 cm radiation) that is regualrly produced by astronomical phenomena, and which has an ability to pass more easily through the clouds of dust in space.  By gauging the direction of most of this radiation, they can infer that the bulk of the galaxy is in the direction of Sagitarius.\n\nAnd really, there is "light" coming from all directions, but most of it isn't in the visible range.  Cosmologists have found what is refered to as the 3K (three "degrees" Kelvin--a very cold temperature) radiation background that exists in direction.  This is seen not as the product of stars, but as a remnant of the big bang.\n\nBut most importantly, there are not really "infinite" stars.  The universe, though boundless, is not truly infinite.  There are some mathematical oddities that you find when you try to deal with the infinite and the boundless.  For instance, there are an infinite number of poritive integers, and there are an infinite number of irrational numbers between 0 and 1.  As odd as it seems, there are actually more irrational numbers between 0 and 1 (what my math professor called the "uncountably infinite") than there are positive integers (so-called "countably infinite").  Due to the relativity of simultneity shown by Einstein, one cannot exactlt quantify the total number of stars in the universe at a given point in time, because an observer moving at a different speed and looking at that moment in time would disagree as to which stars had already exploded or not, and which stars had already formed or not.  So while you can really make a definitive statement as to the number of stars, the number is not really infinite in the general sense of the word, as neither is the universe truly infinite.
892719
It's radial motion away from us - orbital would be around some central point, which the universe doesn't have (a gravitational center, at least) - although galaxies usually have some particular velocity within their clusters.
1157446
The reason nothing is sent out from earth up or down is rather simple, Nothing is within reach in those directions. For the most part the planetary system; the only thing we are able to explore at current technology level, is on a flat planer system due to the suns gravity force. Certainly the universe is tri-dimensional but it is A: very hard to depict in that way. and B: Impossible for us to study in terms of anything besides telescope observation.
455949
everything in this universe moves. stars are parts of galaxies. for example our sun is a part of the milky way galaxy. we are in the sagittarius arm of our galaxy which rotates about its centre and as we are in one of the outer arms as the galaxy seems to rotate the sun along with its nine planets revolves around the centre of the galaxy. this is exactly what happens in other stars and star systems. secondly  all stars are round not to mention, every heavenly body is round because gravity makes them round. and the shape we concieve is just because of the phenomenon of scattering of light as the light from the stars passes through various layers of the atmospheres of different densities
763882
A galaxy is a swirling collection of stars. our own Milky Way galaxy contains hundreds of billions of stars, of which our sun is only one amongst these billions and billions.\n\nA solar system is just a single sun that has planets revolving around it. A galaxy is made up of billions of such suns. And some scientists believe that as many as 25% of the stars could have planets. That means billions and billions of solar systems in our own galaxy.\n\nHere'a a picture of our closest neighbor, the Andromeda galaxy. It has close to one-trillion stars.\n\nHope this heolps. Cheers\n\nhttp://en.wikipedia.org/wiki/Andromeda_Galaxy
1130599
The planets in this solar system are in stable orbits and get no farther away from each other than their orbits allow.\n\nYou are thinking of things like galaxies moving away from eachother, indicating that the universe is expanding.\n\nFirst off, to correct a misconception, some galaxies are moving towards one another, for example, the Andromeda Galaxy, and our own galaxy the Milky Way. \n\nCertain galaxies also seem to be "clumping" together, traveling towards something called "the geat attractor".\n\nDistant galaxies and quasars seem to be moving away.\n\nTo answer your question, some speculate that the expansion of the universe will continue forever and that gravity will lose in the long run. Eventually clusters of matter will become so seperated from eachother that the possability of any productive interactions approaches zero and stars will eventually die, and their remnants will be spread to thin to form into new ones. The universe, will essentially be a cold, dark, corpse. This is called the "cold death" theory. Depressing isn't it?\n\nBut never fear! There are other theories out there! Perhaps the universe will eventually implode into a big crunch, and the force of this implosion will create a new universe! Scientists aren't yet sure exactly how the universe will end. Hopefully none of us will be around to find out by example.
24590
The universe may or may not have a large three or four demensional structure, but it more than likely has an overall natural curvature based on it's density.  If the density of the universe is enough to overcome the expansion of the big bang, than general relativity predicts that space will have a possitive curvature, like that of a sphere.  If it's density is less than the expansive force of the big bang it will have a negative curvature, which is impossible to model in three dimensional space, but is often described as saddle like.  If the density is exactly right that the universe will slow in its expansion forever and never re-collapse, then space is probably flat.  This site could help...\n\nhttp://en.wikipedia.org/wiki/Shape_of_the_Universe
1057373
When we look toward the galactic center we see a long, thin strip. This suggests a disk seen edge-on, rather than a ellipsoid or another shape. We can also detect the bulge at the center. Since we see spiral galaxies which are disks with central bulges, this is a bit of a tipoff. \n\nWhen we measure velocities of stars and gas in our galaxy, we see an overall rotational motion greater than random motions. This is another characteristic of a spiral.
6752
Blue shifting galaxies are ones that are headed more towards us than away. The spectrum we see from a galaxy is a combination of its more or less random speed relative to us due to interations with other galaxies, and the redshift from the expansion of the universe.\n\nUnless a galaxy is very close, the redshift expansion will dominate so that only redshifts are detected.\n\nThe big exception is the Andromeda galaxy, which is a spiral just like the Milky Way galaxy, and a "mere" 2.9 million light years away and is the closest big galaxy to ours. \n\nIn terms of being worried about it well...Andromeda is heading out way, and well collide with the Milky Way Galaxy in about 4 billion years or so.\n\nThat means is one were to stand on Earth or Mars the sky would be increasingly taken up by the fuzzy blog of Andromeda until suddenly (relativity speaking) the whole things is a huge explosion of stars.\n\nNot a literal explosions. Stars are very far apart from each other relative to their size, and about zero stars will actually collide.
843281
They are the first abnormalities in the universe.  These ripples are places where there was more/less energy then other places in the universe when it was very young.  Thanks to them, gravity was more dominant in some areas and less dominant in others allowing galaxies and things to contract under their own gravity and form.  If the universe was perfectly uniform, it would just be a sea of particles today.
1061786
There are actual images of the entire galaxy, but from our position within the disk, it looks a lot like an edge on thin disk with a galactic bulge.  The earliest image of our galaxy that I know of was assembled from IRAS data.  The DIRBE experiment aboard COBE also produces a some nice ones (COBE was a mission to explore the microwave background radiation left over from the big bang.  DIRBE was aboard that spacecraft to characterize the diffuse infrared foreground, namely our galaxy, so its contribution could be removed from the microwave measurements).\n\nDIRBEs shorter wavelength infrared channels trace the stars in the galaxy nicely so you can see the bulge:http://antwrp.gsfc.nasa.gov/apod/ap000130.html\n\nThe longer wavelength channels are more sensitive to dust:http://antwrp.gsfc.nasa.gov/apod/ap000517.html\n\nNote that these are all sky images probably using a Molleweide projection.  The centers look towards the center of the galaxy, but the edges look directly out (away) from the center.  This is a "wraparound" view.
777198
the Milky Way is a galaxy
749553
The Universe is expanding, but individual galaxies are not expanding.  So the stars within a galaxy aren't getting farther apart from each other.  Similarly, our solar system is not expanding (many people get confused about all that).\n\nIn fact, even galaxies within a cluster of galaxies aren't moving apart from each other - for example, the Milky Way galaxy and the Andromeda galaxy are moving *towards* each other, and will collide in a few billion years.  It's the clusters of galaxies that are moving away from each other.\n\nEven though the galaxy itself isn't expanding, the stars are all moving relative to each other.  They all rotate the center of the galaxy, and they also have random motions.  So (as other people above have said) the constellations as we see them today will change - their shapes will become more and more distorted over time.  Here's a neat website which shows what the Big Dipper will look like in the future: http://www.fourmilab.ch/yoursky/help/proper.html
927930
Look up "the nebular hypothesis".  you also are confusing the Milky Way (a disk shaped system of a hundred billion stars or so of which our sun is a part) and the Solar System (our sun and its surrounding planets and other assorted detritus.)\n\nhttp://en.wikipedia.org/wiki/Solar_nebula