See my copyright notice for fair use practices. Determining the structure of our galaxy is not an easy task because the solar system is stuck inside the Galaxy and we can only look in all different directions. The fact that you see a narrow band of stars tells you that our galaxy is shaped like a thin disk. If we lived in a more spherical galaxy, the stars would be distributed more uniformily around the sky. There is a hint of a bulge in the direction of the Sagittarius constellation.
Careful star counts and determining their distances shows hints of a spiral pattern in the disk.
The interstellar dust limits our view a small section of the Galaxy. However, clear evidence of the spiral structure in the disk comes from the 21-cm line radiation discussed in the previous section . Our galaxy, the Milky Way , is disk-shaped with spiral arms in the disk. It has an elliptical bulge in the center and a spherical halo that is denser closer to the Galaxy center. It is about 100,000 light years across and our solar system is about two-thirds of the way out from the center.