Per

I don't know much about astronomy so I have a few questions if any of you do.

Ok, so galaxies are composed of star systems, right? And because of the expanding nature of the universe (right?) the galaxies are moving away from each other.
So, what's in between the galaxies, is it just empty space? And how far is our galaxy from the nearest neighboring galaxy in proportion to it's own size?

(I've always wondered why other galaxies were (practically) never mentioned on Star Trek )

Jesus Tap-Dancin' Christ

Oh, it's more than empty space between galaxies. It's nothing. Empty space composes most of everything (less than .0000001% of you is actually filled), and in space, even that slim margin isn't there. And that goes true for within galaxies too.

Isn't this better off in Science and Skepticism?

Per

Ok, I think I know what you're saying here.

Btw, can stars in other galaxies be observed from earth, and if so, how does one know they're are in another galaxy and not just in the other end of our own?

Oh right, didn't think of that. :banghead:

Mageth

The Andromeda galaxy (M31) is about 2.9 million light years away from the Milky Way.

The Small Magellanic Cloud is approximately 210,00 light years distant.

The Large Magellanic Cloud is approximately 179,000 light years distant.

The Sagittarius Dwarf Elliptical Galaxy is only 80,000 light years from the Milky Way.

The Milky way is estimated to be about 100,000 light years across the disk, and 10,000 light years thick.

That means that M31 is about 29 Milky Way diameters away (and, BTW, some think it's headed our way for a possible collision with the Milky Way. Don't worrk; that wouldn't be for a few billion years).

An interesting link:
The Messier Catalog.

Per

Thanks, Mageth, really puts it into perspective.

Do they know why the M31 is allegedly headed towards us? Has something changed to make it change direction or something?

Those clouds, what are they made of?

Mageth

Individual stars in other galaxies generally can't be observed optically from earth (though some in nearby galaxies can be individually resolved), though there is the occasinal supernova (and another). Radio, x-ray, etc. can be used to detect individual ones of some other kinds of stars (e.g. pulsars).

As far as determining distance,
a lot of different methods may be used.

Mageth

Those clouds, what are they made of?

Both Magellanic Clouds are irregular dwarf galaxies orbiting our Milky Way galaxy, and are made up of stars, interstellar gasses, etc. just like other galaxies.

See here.

Mageth

Do they know why the M31 is allegedly headed towards us? Has something changed to make it change direction or something?

One theory is that the two galaxies were close enough together that they became “gravitionally bonded" and thus began to draw closer to each other.

Here's an example of what it might look like (this wouldn't be the first such collision).

Demosthenes

The Magellanic Clouds are made out of stars and gases just like our galaxy. The reason they're names clouds is because they're irregular galaxies and then the early explorers in the south hemisphere(the Magellanic Clouds can only be seen in southern hemisphere) first saw those galaxies they mistook them for some kind of celestial clouds.

In the intergalactic space there are cold diffused gas and dust and streaming photons.

We can tell that M31 is headed our way due to the blue shift of light coming from the galaxy which indicates that it's moving towards us. Galaxies are constantly in motion, it's inevitable that some of them will collide. Gravity of our both galaxies will also serve to pull each other into themselves. But no worries, it won't happen for at least 3 billion years and plus there's a very little risk that stars in either of the galaxies will actually collide because the distances between individual stars are great enough to minimize any collisions. Sure people still around will be treated to a spectacular view as the heavens are rearranged and all kinds of new star formations take place due to the compressed dust clouds as both galaxies plow into each other. The new resulting elliptical galaxy will be vastly larger and thronged with hundreds of blazing new blue and yellow stars along with two supermassive blackholes from both Milky Way and Andromeda galaxies in the center. Depends on where the solar system end up, we might get blasted by all kinds of radiation from the new stars and as well as an active galactic nucleus.

I kinda wish that we had emerged during that future epoch instead of present time. We'll probably be able to accumulate million times more astronomical knowledge as well as be treated to literally heavenly sights than if we were living in today's quiet and mature galaxy.

Our Local galaxy cluster is in turn moving towards the Virgo cluster which is the center of the Local supercluster. Although I seem to recall that some astronomers think that our Local cluster is also being tugged on by the Great Attractor in another direction. They don't have enough data to determine who will win the tug of war.

Autonemesis

Oh yes, the latest "deep field" image from the Hubble captured millions of outlying stars that belong to the Andromeda galaxy, M31.

See here: http://hubblesite.org/newscenter/archive/2003/15/

We know they belong to Andromeda because of their extreme faintness. They can all be readily identified as normal Sun-like stars by the distinctive signature of such bodies exposed in their spectra. There are very few galaxies close enough to the Milky Way for even Hubble to image the constituent stars as discrete pinpoints in an image. M31 is one of them, M33 is another large spiral in the Local Group where stars can be imaged, as are the Large and Small Magellanic Clouds, visible from the tropics and points south. There are a few dozen other small galaxies in the Local Group where individual stars have been imaged, and with special techniques under limited circumstances, individual stars have been imaged in farther galaxies - but not much farther.

If these stars were in our own galaxy, they'd be much brighter. That they are so faint can only be explained by their lying at extra-galactic distances.