eli5 How do we know how our galaxy looks like if we’re part of it ?


We can only see ourselves if we look in the mirror or our photos or like we can see how our planet looks because of the satellites . But how can we see our galaxy

In: 10

We can see the disk of our galaxy in the night sky…there is a thick band of stars running around us in a circle (that’s where the name “Milky Way” came from). So we know that we’re inside a relatively flat structure. One side also looks thicker and brighter than the opposite side, so we know that one side is toward the center and the other is toward the edge. We can also see other galaxies and infer from them what galaxies tend to look like; ours does not appear to be special.

The same way we could draw the shape of a house even if we were trapped inside it. We don’t have any “photos” of it from way outside, but from where we sit we can measure the distance to many many different stars and turn them into a rough map that shows us the shape and size. Then an illustrator or computer draws a pict based on that map

antithesys’s answer is great. I just want to emphasize that, just as you suspected: **We can’t** see our galaxy. We are inside it, and nothing ever launched by humans has come even close to leaving it. So we have no photos of it, you’d have to be outside for that. Any image you have seen of “The Milky Way” is not a photo, it’s a drawing or computer model of what we think it *must* look like from outside, based on what we can see by looking out in different directions from inside it.

I can draw a map of my subdivision even when I’m inside of it. If I had any artistic talent I could even do a painting of it. Same with the Milky Way, you just map out what stars you can pin down, extrapolate the rest, and hand that map over to an artist to do a rendition of it. Which is what the “overhead” maps of our galaxy are, renditions not photos.

Although we can’t do that accurate of a map of the MW because of the Zone of Avoidance. Essentially we can’t see that far into either the arms and barely at all through the core as dust and other stars block our vision after a fairly short distance in any wavelength but infrared.

Your mirror is a good analogy. Kick up a cloud of dust while looking in that mirror. You will still see yourself and a lot of dust particles. The density of the galaxy is so low that we can see a good percentage of it even though we are in it. We can calculate where these things are and where they are going accurately enough to build a model of it. It may be easier to grasp if you think about the solar system. We are also within that but have a very good idea of what it looks like.