We don't have any real picture of the Milky Way galaxy. Most non-illustrated images of the entire Milky Way spiral are actually of another spiral galaxy called Messier 74. It's impossible to take a full photo of the Milky Way's spiral structure because it's about 100,000 light-years, and we're stuck on the inside.
No, it isn't. For one thing, we'd have to be outside our galaxy to take an actual photo. In addition, dust scattered throughout the disk blocks most wavelengths of visible light within a distance that is only a fraction of its overall size. However, by using other wavelengths we can map the positions of various types of objects more or less accurately, so we have a pretty good idea of what it would look like if we could see it from the outside. In fact, in some ways we have a better idea of what it looks like than other galaxies, because the mapping techniques used work better up close than at extra-galactic distances.
I'd have to look around a bit to find the best current visualization of what the galaxy would look like if we could see it from the outside, but can tell you that it has a central bar (which was a surprise) and may have a slightly X-shaped nucleus. Given that sort of information, we can look at other galaxies and say (with reasonable but not absolute certainty) that such and such a galaxy probably looks about the same as ours (e.g., M74, as you pointed out). But you are right in assuming that ours doesn't look exactly like the other one. It's sort of like pictures of dinosaurs. Their bones tell us a good deal about their approximate appearance, but whether they had feathers or scales, rough or smooth skin, were brightly colored or just blended into the scenery is usually left to an artist's imagination Similarly, any "image" of our galaxy based on mapping techniques,. no matter how accurate it might be in its overall structure, is not going to be the same as an actual photo
Guembo,
>Is it possible to take a "full" photo of the galaxy ?
Yes.
One simply (!) needs to have a vantage point sufficiently far from the plane of the galaxy. It's not easily done, but it is certainly *not* impossible.
In lieu of that, as Courtney suggests, in-plane measurements at a variety of wavelengths allows one to deduce the crude structure of the local arms of the galaxy.
COBE image:
https://parade.com/wp-content/uploads/2014/01/COBE-infrared-image-of-the-Milky-Way-vtr.jpg
Thank you, dear Courtney Seligman. It's clear that we have a representation of our Galaxy. I found your answer comprehensible.
Thank also to James Garry.
Is it possible to read scientific papers related to my question?
Guembo,
Naturally.
The NASA ADS shows me 8172 abstracts for a search 'milky way structure'.
These are tips of the iceberg:
http://adsabs.harvard.edu/abs/2017arXiv170601900F
http://adsabs.harvard.edu/abs/2017arXiv170600018M
http://adsabs.harvard.edu/abs/2017arXiv170500425W
(all from: http://www.adsabs.harvard.edu/)
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