There has never been a photograph taken of the Milky Way galaxy. It would take centuries to get a probe far away enough to capture its shape. Yet we have artist's renderings of the galaxy like the one above. How can we possibly know the galaxy's shape when we are inside of it? The truth is that we don't know, but we are learning more about it all the time. The premise we start with is what we can observe. What we see in the skies as the Milky Way is a band of distant stars, which are the nearest of the hundreds of billions of stars in the galaxy. That suggests the galaxy is disc-shaped. While we can't see our own galaxy as a whole, we can see other galaxies, and those that are disc-shaped tend to have arms moving in a spiral. So we can assume that the Milky Way also has arms in a spiral. But that is old news.
With ever more powerful space imaging technology, we are making discoveries that give us a better idea of what the Milky Way looks like. The movement of the stars we know suggest what is hidden behind them by space dust and signal interference. Radio signals penetrate that dust and can map hydrogen gas between stars. There have been many breakthroughs that reveal the size, shape, and texture of the galaxy without us ever seeing what we are studying. Read about the technology that shows us more and more of what we cannot see at Sky at Night magazine. -via Damn Interesting
(Image credit: Nick Risinger)