How do we know the shape of our galaxy?
We think of our galaxy as being shaped like a big pinwheel. Yet we’ve never sent a camera outside of our galaxy to get an ‘outside view.’
We can’t travel outside the galaxy to take pictures. A space probe moving at near light speed would take thousands of years to get far enough away to take a parting snapshot.
But we can infer the shape of our galaxy by looking outward into space – toward tens of billions of other galaxies. Our universe makes galaxies only in only a few basic models. The most common are spiral or disk-shaped galaxies – and we believe our galaxy is one of these. Like snowflakes, though, no two spiral galaxies are exactly alike. So we may never know exactly what the Milky Way looks like from outside its boundaries.
One fair example of what our Milky Way might look like is the neighboring Andromeda galaxy. It’s believed to be sort of a celestial twin to the Milky Way. Any civilizations in Andromeda might now be peering our direction across 2 million light-years of space. They might be wondering if their galaxy looks like ours.