They connect aliens and flying through space with it. Here it is, simple yet direct. Astronomy is the study of the universe and what it beholds. That means, the person looking through a telescope is an astronomer. Professional astronomers are the ones that provide us with breath-taking images of nebulae, galaxies, planets, I won't get any more specific.
Cosmology is the study of something a bit more complex, like the origin of the universe and time.
Now that you're a bit more enlightened, think twice before you ask an astronomer why they want to fly in space. This may not apply to many people . First create, then execute. Used under License.