Galaxies are very large and distinct communities of stars. This is where star formation is primarily found. It was generally believed that most of the galaxies we see were nebulae, until Hubble proved, in the 1920s, that the Great Andromeda Galaxy, M31, lay far out side of our own galaxy. Lord Rosse was the first to notice the spiral pattern in a galaxy when he viewed the Whirlpool Galaxy, M51, in 1845 through his gigantic reflecting telescope in Ireland. There are about 100 stellar clusters in our galaxy that formed at the same time as our galaxy.
Globular clusters appear to contain the oldest stars in the universe.
A moon is, astronomically, very similar to a planet, except that instead of orbiting the Sun, it orbits a planet. Our moon always presents the same side to the Earth because it rotates on its axis once during each orbit of the Earth. The lunar phases are caused by its position in space relative to the Sun and the Earth. The best time to view the moon is when it is in a crescent or gibbous phase, when shadows are longest. The stars that comprise them are usually young stars that formed out of a common cloud of interstellar gas and dust.