How did we map out the exact shape of the Milky Way, given that we can’t see all of it at once? Or more importantly, how sure are we that we got the shape and size right?

Question

How did we map out the exact shape of the Milky Way, given that we can’t see all of it at once? Or more importantly, how sure are we that we got the shape and size right?

In: Planetary Science

Answer 1

We know a lot about gravity and mass on a galactic scale from looking at other galaxies. From that we can calculate a lot of the data we can’t directly observe