Spiral galaxies are a type of galaxy characterized by their distinct spiral arms that wind outward from a central bulge. These arms are made up of stars, gas, and dust, and they often contain regions of active star formation. The Milky Way is a well-known example of a spiral galaxy. The structure of spiral galaxies is typically divided into three main parts: the central bulge, the disk, and the halo. The bulge contains older stars, while the disk is where most of the galaxy's star formation occurs. The halo surrounds the galaxy and contains dark matter, which helps to hold the galaxy together.