Galaxies
Galaxies are vast associations of stars.
Galaxies are classified by their shape. There are three distinct shapes, spiral, elliptical and irregular, with several variations within each classification.
We observe galaxies in every direction we look. The plane of the Milky Way contains vast tracks of dust which obscure of view of galaxies, so our best view is in directions away from the plane.
NASA's Hubble Space Telescope showed the depth of the galactic population by producing an very special image, shown below. By staring at an area of the sky where we had previously observed nothing, and remaining focused on that area for a whole month, we were able to find that the further we look, the more galaxies we see.
