Space is 3D

Q:

It seems like we only ever speak in horizontal terms when referring to space. What happens when we go straight up? Are there other galaxies way above us?

- Graeme S.

A:

Space is (more or less) "isotropic" - that is, on a large scale it's pretty much the same in every direction. "Large scale" means "huge groups of clusters of huge numbers of galaxies" - on that scale, if you point in any direction you'll see about the same number of galaxies.

On a smaller scale it's a bit different: our solar system is actually very flat. That comes from the way our solar system was formed: we started off as a big blob as gas which contracted into a small blob of gas. The initial big blob of gas is going to be spinning a little - just because if you take a bunch of random gas the odds that it's perfectly still is pretty much zero. As it contracts, it starts spinning faster and faster - this is just the conservation of angular momentum. The spinning makes the gas blob stretch out into a thin pancake, which eventually turns into the Sun and the planets, which stay in a nice flat plane as well. Something kinda similar happens with the Milky Way, our galaxy, as well - so both our galaxy and our solar system have most of their material in a fairly flat shape. Once you go beyond our galaxy though, all the other galaxies are pretty much all over the place - in fact, two of the closest galaxies, the Magellanic Cloud are pretty close to straight "down" from the plane of the Milky Way.

One more thing - even though most of the stuff in the Milky Way is in the flat plane, that plane is thousands of light years thick. There's also a good number of "halo" stars - stars in a more sphere-type shape, nowhere near the flat plane. The dark matter is also supposed to be spread out in a pretty much spherical shape as well.

That help? :) Keep asking questions!