Considering sending a probe into intergalactic space would take many millennia to get a broad enough vantage traveling above/below the galactic plane, it’s certainly not anything to expect to see within our lifetime (as an understatement).
Considering current and promising future tech, what would it take to directly image our Galaxy?
And what techniques can be used as indirect ways to paint in the details with as much accuracy as possible—while we wait for the probe’s email?
Directly? Pretty much not possible with any tech we can imagine.
Indirectly? The same way they’re doing it now.
Because we are kinda on the outside of it, we can see most of the Milky Way right from where we are. All you need to do is map out the stars and their distance from us and that will give you a rough picture of our galaxy. We can fill in the blanks with a bit of guesswork (compare what we have to known similar galaxies) and then once we have our model of our galaxy, all we need to do is rotate it and we can tell what it would look like from a different vantage point.
It looks like this:
http://www.sslmit.unibo.it/zat/images/cartography/M-Way_2.htm
Which part of the galaxy appears as the “Milky Way” in our night sky? Is it pretty much all of it other than the stars close to us?
Every individual star you can see with your naked eyes is part of our galaxy. Our galaxy is a flattened disk, like a Frisbee or a fried egg. When you look along the central plane of the disk (which is where the majority of the galaxy’s stars are found), that’s where you see the ribbon of light we call the Milky Way. That ribbon is brightest when you look in the direction of galactic center (the egg yolk in a fried egg), and faintest when you look in the direction 180 degrees opposite of the galactic center.
So, pretty much, “Yes.” Except for the stars closest to us and “behind” us, the Milky Way represents the vast majority of stars in the Milky Way Galaxy.
Correct.
If you can picture yourself a tiny germ on a clear glass plate with (actually in it) hundreds of billions of soot particles, concentrating at the center… then you’d be about ⅔ of the way out from the center, looking toward and through the center of the plate (= summer time), and looking out through much less glass at the rim (= winter time).
Obviously, when looking at the center of the Milky Way, you’re seeing our galaxy edge on, but from within it. So looking toward the center, and whatever 50,000 LYs worth of stars lay beyond (plus gas and dust) is really the “glow” of the Milky Way.
And of course, any individual star you see in the night sky, is really in our local neighborhood.
Over the next few years we’re going to get a far more thorough and precise map of the milky way, thanks to the recently-launched Gaia satellite.
Also the OP might be interested by this interactive visualization (warning: it plays music) of everything from the scale of our solar system to the entire galaxy. We’ve got very precise surveys of thousands of stars in our local neighborhood, but on the scale of the entire galaxy there will be a lot of guesswork and artistic license, particularly on the opposite side of the milky way. Hit the little graph icon in the top right and it shows you a point for the mapped stars showing position and temperature.
If there were a habitable planet on the outer edge of the disk of our galaxy, would they see stars in half the sky but not in the other?
Right exactly on the edge, to the extent that’s meaningful, yes, though individual stars would be pretty sparse even on the inward side. Merely very near the edge, though, the starfield would probably look much the same in any direction. Of course, in either case the band of the Milky Way would be much less prominent, if visible at all, from the outward side.
The Galaxy has about the same ratio of thickness to diameter as a CD, and the limit to stars we can see individually with the naked eye is only a slightly greater distance than the thickness of the disk. So if you’re even one disk-thickness in from the edge, it’ll still look like you’re in the thick of it.
Astronomers aren’t even sure if the Milky way comprises of two or for spiral strands, source BBC2, however I’m sure this will improve as we become more adept at non-visible light ‘RF’ Telescopy.
As for getting an external oblique view of our galaxy, well its between 100,00 and 120,00 light years in diameter so working on the premise of the speed of light it won’t be soon!
Peter
A nice basic map can be found here, but it is quite speculative in many ways.
http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=8083
Even nicer is this one by National Geographic
http://maroonbeard.com/wp-content/uploads/2012/09/The-Milky-Way.jpg
This downloadable mapping program by the American Museum of Natural History’s Hayden Planetarium is very nice indeed, although the controls take a bit of getting used to.
http://www.amnh.org/our-research/hayden-planetarium/digital-universe
Consdiering that it took 35 years for Voyager 1 just to leave the Solar system, I think it is pretty unreasonable to expect anything we make to be leaving the galaxy any time soon, let alone being able to send a picture back.
More links!
This website is all about the science of mapping the galaxy. It includes some excellent astronomy-101 level explanations about the types of techniques that can be used to measure the position and velocity of objects in the galaxy, their limitations, and many specific astronomical datasets. I’ve spent a few hours reading there already…
I have occasionally wondered how long a spacecraft travelling perpendicular to the plane of the solar system would have to go in order to send back any useful data on…well, anything. Presumably it’d have to be a fair ways away even to send back decent top-down (or bottom-up) pictures of the solar system.
Speaking of which, and on a lighter note, this is my current favorite graphic demonstrating our place in the universe.
I’ll have a stab at answering the first part of the OPs question directly - even though I’m probably not qualified to. Mainly because it’s interesting to me and I’m interested to see if anyone has anything to add or correct.
Accuracy shouldn’t a problem, getting the probe to a point above the galaxy would be very straightforward - you’d have an enormous target area in which to point the probe so that would be easy.
The next problem would be the time it takes. Voyager was able to get a decent slingshot from a rare alignment of planets. Without that the probe would travel more slowly and we already know that Voyager is only just reaching the edge of the Sun’s influence. even with a fantastic sligshot it would take epoch-spanning years for the probe to reach the required distance (even with a super-duper wide angle lens).
Which brings us to life span. The probe would need to be built to last all those centuries. To withstand all the things that space throws at it. I’m not sure about this, but I’m guessing this would challenge us greatly. Maybe someone else knows more, but the engineers could set the path of the probe through a quiet part of space away from other stars to minimise radiation and so on.
Seeing as it’s going to be a long long journey, we need to power the probe. A piece of radioactive material might be harnessed to provide energy. Voyager turns radioactive thermal energy into electrical energy but I read that it will be forced to power down it’s last instrument no earlier than 2025. Perhaps it will exceed this by a decade or two, but that’s still not nearly long enough for our probe. Undoubtedly our technology will have improved and the half-life of some materials can be measured in hundreds of thousands or even millions and billions of years. Can we harness these enough to power our camera and communications? I don’t know, perhaps someone else can enlighten us.
And so… communications. Obviously the probe will be so distant at this point that any idea of two-way communication would be utterly ridiculous. So the probe will shout it’s information back to us and hope we can hear. Or, in fact see. Because I don’t think radio communication will cut it. This probe, I think, will need laser light communication. Which isn’t perfected yet. Although it’s surely not an insurmountable objective. And the probe would have to know where to point it’s laser. We might need to map the galaxy to a fine level of accuracy to allow the probe to look around and orientate itself. (Which would make taking the photo redundant, but hey we’re just trying to work out of we can do this right?) More power required. And the mechanisms to manoeuvre the craft and to remove the lens cap, to actuate the camera shutter or anything else would need to have lasted through all this time. In space.
That’s the probe. On a more practical level we’d have to ensure that the probe does not get forgotten. That we remember to look. The probe might contain a timer so we would be able to calculate the exact time we need to start looking for it. The sort of timelengths we are talking about are longer than the life expectancy of almost all of our storage technology. Instructions to look, how to decode the code the probe sends, and other technicalities might have to be passed down through the generations.
Finally, we would probably be able to invent better and better space craft which would be able to overtake our ancient probe. By the time the probe gets to it’s destination it might find a human colony of space archeologists, eagerly waiting for it’s arrival.
Without doubt I’ve failed to consider a very long list of requirements. I’m not a space engineer! BUt it was a fun to have a think about it… 
I vaguely recall hearing that extremely high vehicle speeds were once envisioned with the use of ion thrusters. They won’t work to get a rocket off of the ground, but once you’re out in space, their gentle push can be sustained for days/weeks/years, eventually propelling your cargo at something like 100,000 MPH.
Here’s the problem:
The Milky Way galaxy is about 1000 light-years thick, and 100,000 light-years in diameter. I can’t find what our solar system’s location is in the z-direction, but if you assume we’re right on the central plane, then our cameraman has to travel 500 light-years just to get to the edge of the galaxy. At 100,000 MPH, that’s going to take about 3.4 million years.
If you want to get high enough above the galactic plane to snap a photo of the entire Milky Way using a camera with a 90-degree field of view, then you’ve got to travel anough 50,000 light-years, and that’s going to take another 340 million years.
You’d better bring a snack.
If you want to transmit the image back to Earth via radio waves, tack on another 50,500 years before the signal arrives.
