Astronomy is the science that studies stars, planets, moons and space in general. It studies and observes not only space and all the objects contained within it but also celestial phenomenons such as the creation of supernovas, black holes, shooting stars or asteroids getting too close to planets. Astronomy is very closely related to astrophysics too, which as it name indicates is more concerned with the physics of space and spatial objects while astronomy concentrates on the composition, behaviours, properties and motions of the spatial objects.
Astronomy is very closely related to astrophysics
A lot of people divide astronomy into two branches of study: the observational and the theoretical. The observational focuses on observing planets, stars, asteroids, moons and studying their behaviours on isolation; while the theoretical analyzes all this elements as part of a system (for example, the Solar System , the Milky Way or a galaxy) and studies how this systems and clusters may have been created and evolved.