Spiral galaxies have yellow bulges at their centers and flat, blue-white disks, comprised of stars, gas and dust. Spirals can be divided into two groups: normal spirals and barred spirals. In barred spirals, there is a bar of stars running through the central bulge, and the usually start at the bar edges instead of the bulge. Spirals are active star-formers and make up most of the galaxies in the local universe.

Elliptical galaxies account for about one-third of all galaxies, and their shapes vary from nearly circular to very elongated. They possess little gas and dust, and the stars in them are older and not actively star-forming. The largest and rarest are about 300,000 light-years across and were formed by the merging of smaller galaxies. More common are the dwarf ellipticals, and those are only a few thousand light-years wide.

Irregular galaxies have very little dust and are neither flat (disk-like) nor elliptical. Astronomers often see irregular galaxies as they peer deeply into the universe, which is equivalent to looking back at the early Universe. They were abundant back then, before spirals and ellipticals developed. Many of them are caught in the process of merging of two smaller galaxies, which is how they get their interesting shapes.