Position of Stars, and the shape of the known Universe

Originally posted by stumason
So, assuming still that the stars (for arguments sake) don't speed up or slow down, but travel constantly, Astronomers are just plonking them on a map based solely on their relative distance from Earth, not taking into account their motion or the amount of time the light has taken to reach us?

I think that that is generally correct. THere is no way to know what their motion is going to be, so there is no way to know what there motion has been in the time between when the light left the star and when it reached the earth. They can get information about what it is 'now' (or rather, now in the image they get of it), and say 'its traveling at X, therefore its probably X(time) distant from the visible position. I wouldn't know for sure tho.

As far as everything being plotted relative to earth, well, whats wrong with that? Any point is going to be just as good as any other.

You have not answered my question on wether anyone has actually taken into account distance for the light to travel, and motion of the body during the time it has taken the light to travel to earth

I'd be surprised if they actually did this. It seems uncecessary, since there are not star-devices like you were hypothesising. if I want to see whats going on in abu dabi, I'd look thru my super telescope and figure it out. If I wanted to go to abu dabi, i need a different system altogether. Since no one is going there, there's no need to make maps as if they would.

Also, you noted 'real position'. There is no real position. There is no center of the universe, and there are no detectible edges to the universe, so there can't be, say, 'Universal Coordinates'.

partyof1
But, back to my point, because we use that same type of measurement with all calculations (to form the picture), the picture is accurate.

A map of the universe made by humans does not correspond to an outsiders view of the universe. I can't take a map of the universe made by humans on earth, jump outside the universe, and overlay it onto it and have it match. I can put the point that is earth over earth, but none of the other points will match, because humans have no idea where anything really is, they only know where it was a long time ago.
This is correct no?

understand the mechanics behind measuring the universe, what I do not know is wether the map of the Milky Way (or whatever) is a picture of now, then or a combination of "thens", as each stars light has taken a different amount of time to reach us.

I'd be surprised if they made maps of the universe with that much accuracy. CMB maps, sure, but star maps? For what purpose?
Also, as far as it being 'mutlple thens', I dont see how. A million years ago the stars had a 'real' position. They shot their light off. The light from stars that were a million Light years away from earth back then is just reaching earth....now. In that time, earth has moved and so have they and this results in various red shifts. But there's only one 'then', not multiple 'thens' when you look at the sky.

We will just ignore the stated fact that everything is apparently moving away from everything else, and draw a map of a static galaxy."

I would have to say that, sincethe general public is aware that the universe is moving, that the astronomers from which the public has learned this are also aware. But again i doubt that anyone has taken the time to process a 'right now' map of stars.

That would be different, as the stars further away would have had greater opportunity to change their apparent positions in the time it takes for light to travel to us, more so than the stars that are closer

WHy would more distant objects be moving faster?

We're going to have to do some re-caculations when we finally figure out Interstellar travel

Defintily.

As for the shape of the universe, here are some references
www.nature.com...
www.nature.com.../news/1998/981126/full/981126-4.html

and lemme try the uploader
shape of the universe
Timeaus on the universe

All were these search results.

in ~3 billion years the andromeda galaxy is do to crash into our milkly way galaxy. Depending where our solar system is at the time; it could be obliterated almost instantly. Of course then both black holes at the center of the galaxies will feed off each other....blowing everything up.

Here's an odd one...

Many of those stars may no longer even exist for all we know...as we're seeing the light from them or thousands, even millions of years ago!

So here is your answer, the "stars" are mapped in EARTH right now time. And yes you are right "out there" the object that you have seen from the Earth does not exist out in space in the same area.

You can not take a laser or star gate or any other device to travel to the space object from the reference point you have on Earth. And just like you said that star may not even exist anymore as the "map" on Earth is relative only to that time on Earth as matters of distance and time have changed the source considerably.

Same thing goes for that alien race, the signal we may one day receive etc, the chance that the origination source exists or that we could even travel out that far to find it is so minute...

.
I've had the very same question.

But i think the reason it doesn't make a big difference is because the speed of light is SO much faster than the relative speed of everything else. Any position should be (movement vector + other forces [gravity]) * time distance adjusted to be precisely correct. But things are moving so slow compared to light that the angular difference/change is probably [wild guess] than one percent. probably unmeasurably small for most things.

I wonder what would happen if you had an object moving perpindicular across one's scope of vision at something approaching the speed of light, say 0.75 light speed? Would it, due to its speed simply not be perceptible to us using light?

Any reflected or auto-source light would just be so spread out that it would probably be read as background light.

edit: one more thought

As Gazrok mentioned the more interesting changes are the stars that have gone nova, or blackhole or otherwise re-configured, like become binary pairs or fallen apart as a pair.

curious, is it possible to have a trinary star system that is relatively stable?

[edit on 16-3-2005 by slank]

taking into account the vastness and complexity of the unvierse it gets a little mind boggling!

here mabye this will help with visualizations

"in ~3 billion years the andromeda galaxy is do to crash into our milkly way galaxy. Depending where our solar system is at the time; it could be obliterated almost instantly. Of course then both black holes at the center of the galaxies will feed off each other....blowing everything up."


That is actually very unlikely because our galaxies are so spread out.

I mean I know andromeda is moving closer but from what I read on nasa they said that we will pass right through eachother

the collision will be a good thing, the galaxies will merge and form an even greater galaxy. one that will harbor life on an even more massive scale and one that will dominate the universe in a more prominent manner!

Originally posted by Ignorance Is Bliss
I mean I know andromeda is moving closer but from what I read on nasa they said that we will pass right through eachother

That will be the first "encounter"... The whole process may well be lasting a few millions of years, but actually, Andromeda and the Milky Way will "collide", and really that means passing through each other, at a certain speed. That speed will go decreasing until it reaches 0, then they will be going closer again. And after a second "passing through", there will be another one, and so on, and so on, until after a few ones, the centers will attract themselves that much that the whole thing will actually be a brand new one galaxy.

It may be an irregular galaxy, a perfectly spiral one, a new elliptical, noone can tell, but the whole merging process is something that will anyway take years and years, that will trigger events within both of the galaxies (events of the kind of novae, supernovae, star birth,...). If anyone could be an outside witness of it, kind of film the whole process and speed it up to be a movie like a few minutes long, that would be the next Oscar winning thing!

I had to add something to this thread because I had the strangest idea and thought. Most of you will just laugh it off, but I would still have to think, wow, what if it's true?

What if we are in the only galaxy in the universe? What if all the other galaxies are just what we see of our own galaxy since it takes so long for light to get to us? Why do they look different? Well, because you are seeing it in different stages. We would really have no idea of how fast and what direction the galaxy is going in because we would have nothing else to compare it to, if this were the only galaxy. We are just seeing our own galaxy bouncing around and forever changing.

I know, I know, crazy idea, but I just had to put it out there...

Originally posted by SpookyVince
It may be an irregular galaxy, a perfectly spiral one, a new elliptical, noone can tell, but the whole merging process is something that will anyway take years and years, that will trigger events within both of the galaxies (events of the kind of novae, supernovae, star birth,...).

Result is propably massive elliptical galaxy which are in centers of most galaxy groups. (where collisions have happened most often)

Also it would explain why elliptical galaxies contain very little gas and dust clouds. (disturbances from collisions caused them to collapse to stars)

This will probably throw a wrench into some of the concepts here.

Another issue to consider in trying to figure out where everything is, is the speed of light. Now, according to Einstein's special theory of relativity (if I remember right), the speed of light is measured the same no matter what reference frame you are using. That being said, but the rate of passage of time is not constant.

Various thing affect the passage of time, like gravity wells, and speed of travel of the reference frame. We know that. Now as for the speed of light, what is potentially problematic, is that we can only measure the speed of light by calculating its round-trip travel. That is, we measure how long it takes to go out from our location and reflect back to us. Okay, we can do that. But what we cannot accurately accomplish if to figure out how long the light takes to travel in a single direction. By changing our position to observe where the light may be travelling, we alter our frame of reference as well as our time-measuring capability. So we may never be able to accurately know where an object very far from us in space is actually located at a given instance; we can only accurately determine where we see it to be located right now. It's confusing.