Galaxies A galaxy is a system of stars, dust, and gas. These three subtances are held together by gravity. Throughout the universe there are many galaxies. Small galaxies may have fewer than a billion stars.
Large galaxies can have more than a trillion stars.
Galaxies form in different shapes. The four most common kinds of galaxies are spiral, barred spiral, elliptical, and irregular galaxies. Not only are galaxies scattered across the night sky, but are grouped in clusters. If you look at any kind of galaxy you would see the combined light of the stars inside. Telescopes can be used to study galaxies.