The Milky Way
How large is the Milky Way?
Current measurements indicate that the stellar disk of the Milky Way is about 100,000 light-years across and one thousand light-years thick. If the Milky Way disk were the size of a large pizza, then the solar system might be a microscopic speck of oregano halfway out from the center to the edge of the crust. The bar-bulge structure of the Milky Way is about three thousand light-years high and maybe ten thousand light-years long.
If you take into account the dark matter in the Milky Way, its size increases dramatically. Based on current measurements, at least 90 percent of the mass in the Milky Way’s gravitational field is made up of dark matter, so the luminous stars, gas, and dust of the galaxy are embedded at the center of a huge, roughly spherical dark matter halo more than a million light-years across.