Figure 13-1Schematic Diagrams of the Milky Way (a) This edge-on view shows the Milky Way’s disk, containing most of its stars, gas, and dust, and its halo, containing many old stars. Individual stars in the halo are too dim to be visible on this scale, so the bright regions in the halo represent clusters of stars. (b) Our Galaxy has two major arms and several shorter arm segments, all spiraling out from the ends of a bar of stars and gas that passes through the Galaxy’s center. The bar’s existence and the presence of two major arms were confirmed by the Spitzer Space Telescope.