It is very clear from these images, and a bit of detective work, that the Milky Way is a flat system of stars, with a central bulge located in the constellation Sagittarius. So, we know the Milky Way is a very flat system in 3-dimensions, because from the inside, its projection on the sky is a very narrow band of faint stars. We also know it does not have a gigantic nucleus because when we look along the Milky Way on the sky, we do not see a ‘ball’ of light peeking up from the Milky Way. Using our knowledge of the shapes of other galaxies, we easily conclude it must be a version of a spiral-type galaxy with an unremarkable central nucleus. Here is a similar type of galaxy seen edge-on:
— How do we know the Milky Way is a spiral galaxy?
There’s much more information at the site above, I came to this question while watching the new episodes of Cosmos on Hulu. They were showing pictures of another galaxy as an example of our own. Then I had the thought, how exactly do we know that our own galaxy is ‘much like this one’? The answer: we don’t know with 100% certainty (much like most science, lol) but we do have a pretty damn good idea. From what I understand it would take 100,000 years to get into position to take an image our own galaxy, and another 100,000 years to get that image back to Earth.
Spine tingling stuff here.