Stars vary in brightness throughout their lives based primarily on their mass. Many vary in brightness by high amounts later in life. Star Clusters Stars tend to form in loose clusters in the arms of galaxies. Clusters vary greatly in density, number and types of stars as well as age. The youngest exhibit hot new stars with some original gas gust surrounding them.
Some stars form in giant spherical masses of stars.
Often visible to the unaided eye from a very dark sight and many more are visible through a telescope.