We live in the Milky Way galaxy, an immense, flat, spiral galaxy surrounded by a massive halo of stars and dark matter. The disk of stars, gas, and dust in which the Sun resides is fully 120,000 light years across; a soul-crushing distance on the human scale. In the middle of the disk is the central bulge, a lozenge-shaped hub of stars.
How did all this structure come together? We know it didn’t all happen at once, but what were the different chapters in the galaxy’s life? What is the timeline of the Milky Way?