An open cluster is a randomly shaped grouping of hundreds or thousands of primarily young white and blue stars. Depending on the distance to the cluster, an open cluster may appear as an array of many individual stars or as a faint smudge on the sky. You studied nebulae when looking at the Mount Palomar plates in an earlier lab. Nebulae may appear either bright emission nebulae in which stars are embedded or dark absorption nebulae which only block the light from stars behind them. Like open clusters, visible nebulae are located within our galaxy.
Galaxies are familiar as very large groupings of stars.
The Milky Way is our home galaxy, containing about 200 billion stars. Other galaxies are the most distant objects you will observe. With a small telescope, the different shapes of galaxies can be distinguished.