I got a great question earlier today from my buddy Zrinka, and decided to figure out the answer for her, and also for myself. She asks:
Ethan, is it possible to know, or better to say to imagine somehow how our galaxy looks from outside?
What a simple-sounding question! After all, we know what the Earth looks like from the outside: we just go outside of it and photograph it. But the galaxy is too big to do that to; it would take tens of thousands of years moving at the speed of light to get that far away! So we’re left with the option of looking at our galaxy from inside of it, and trying to figure out what it looks like.
It’s more difficult than it sounds. Consider this: what color are your eyes? Mine are the brown shown here; but how do I know? I either need a reflection, another person to view it and tell me the answer, or, I can take a picture and look at it. The problem is, we can try that for the Milky Way, but since we’re in it, all we see is this:
Pretty hard to tell anything with all that junk (we call it dust) in between us and the rest of the galaxy. We can launch a satellite and look with infrared light, where the dust isn’t so important, and that’s what the COBE satellite did with its infrared imager:
Well, that looks a lot like other edge-on spiral galaxies that we see, like NGC 4013:
That’s basically what we’re stuck doing — looking in our own galaxy for the little bit of information we can find, then looking out at the millions of galaxies we know of and seeing which ones match the best. We’ve recently (in the last few years, with the Spitzer Space Telescope) discovered that in addition to the four major spiral arms, the lesser outer arms, and the central bulge, our galaxy also has a central bar about 3 kiloparsecs (10,000 light-years) across.
So now, we know a ton about our Milky Way. But what does it look like to an outside observer? Or, maybe a better question, is of all the galaxies we’ve seen, which one matches up best to the Milky Way? The answer is NGC 7331, which looks like this in the visible:
and this in the infrared:
The other option is to go for the “artist’s rendition,” which just doesn’t do it for me. But in any case, hopefully this has given you a lot of help towards “visualizing” what we look like! If you ever get far enough away to take a picture, you can try to send it to me, but don’t bother; I’ll most likely be dead by then.