We all – even those of us who live in rural areas – live in a great city, one made of stars, our Milky Way galaxy. You can even see it on a dark night away from city lights, a vast, dense cloud of billions of stars that arches from horizon to horizon.
It wasn’t until 1923 when astronomer Edwin Hubble and others discovered that hazy nebulae that observers had been looking at for hundreds of years were not actually within our own galaxy, but were galaxies in their own right. Now we know there are hundreds of billions of galaxies in the universe.
Our own was born some 12.3 billion years ago, about one to three billion years after the Big Bang itself.
We are learning more and more, especially in the last ten years or so, about how the Milky Way formed and evolves. Like other spiral galaxies, our Milky Way has several distinct structural components that probably appeared at different stages in its formation process. The stars belonging to each component have distinct chemical compositions, and they move through the galaxy in distinctive ways. Such differences hold important clues about how the Milky Way formed and develops.