And no, we do not launch a spacecraft out of the galaxy to take images. It would take millennia to get there and send data back home.
The Milky Way is an impressively large galaxy. Its star count is within the hundreds of billions, and it is almost 2 MILLION light years wide if you include the dark matter! Yet, it’s nowhere near the largest we’ve discovered, but it is the second largest in the local group!
What are the pictures we see on the internet then?
In order to image our galaxy head on we’d need a spacecraft to actually leave the Milky Way, and there’s no way for us to do that yet. Our furthest spacecraft, Voyager 1, has been going for 44 years and hasn’t even travelled a light year! Instead, the bird’s eye images we see are all artists impressions.
While bird’s eye photos are impossible to take, side view ones aren’t! There are plenty of these online, such as the one below. If you wrapped that one around into a tube, you can start to get an understanding of what the Milky Way looks like.
Doing this in just the optical provides insufficient information for an artist to create an impression, especially since there’s so much dust and debris that obscures the galaxy. For this reason, we need lower frequency data such as infrared and radio waves.
However, we also want to use high frequency bands like X-rays to know where high energy objects are, such as the gas clouds close to the supermassive black hole, and where young stars are being formed. Since the Milky Way is a spiral galaxy, these young star clusters shouldn’t be found everywhere but mainly in the spiral arms, and we can show this by distance measurements.
Another source of information that is used are similar galaxies. UGC 12158 is thought to be a really good match, and NGC 4921 is sort of similar but in structure only.
Our artist should now be able to build up an idea of the layout of the galaxy!
We think we know, but we don’t actually know
Due to the unfortunate fact that we live in this galaxy, it is genuinely a struggle to observe the Milky Way. Many research papers come to different conclusions on values such as mass (with differences of up to half an Andromeda Galaxy), size, velocities, and the dark to normal matter ratio.
People also forget that it was only 100 years ago that we realised there were more than just 1 galaxy in the universe; We’ve still a long way to go!
A current mission by ESA, Gaia, is a spacecraft designed for highly precise measurements of stellar distance, with the aim to produce a highly detailed and accurate 3D map of as many stars as possible, particularly the ones that make up the Milky Way. From this mission, I’m sure we’ll be able to create the best possible model of the Milky Way (so far!)