The Milky Way we see today is known as a spiral galaxy due to its shape, a flattened disc that bulges in the center. Arms of concentrated matter swirl out from the bulge giving it its spiral appearance. Between the arms of matter are dust lanes, which gives the area a vacant look. The diameter of the disc is approximately 100,000 light years across while the thickness of the disc is only 2,000 light years. The center bulge reaches out to a thickness of about 6,000 light years. The galaxy itself has a well-ordered motion revolving around the galactic center and is surrounded by the galactic halo. The halo is made up of faint older stars that meander randomly, engulfing the galaxy.
The galaxy's spiral arms are formed as the galaxy spins and density waves move through the collection of stars and gas. The waves compress different parts of the disc at different times and give it the characteristic spiral shape. These spiral arms rotate around the center bulge where most of the matter is contained, and as the galaxy spins it maintains its shape through the rotational movement and gravity. The stars and globular clusters in the halo that surround the main portion of the galaxy give it an overall spherical shape.
The discovery of the Milky Way is a relatively rec