Astrophysics is a science that uses physics and chemistry to create theories about the formation, destruction and nature of planets, stars, galaxies and other interstellar bodies. It is closely related to and often confused with the two other main branches of space science: cosmology and astrology.
Generally speaking, astronomy measures the specific positions, movements and characteristics of interstellar bodies, whereas astrophysics attempts to determine more about the nature or physics behind these features. Cosmology is closer related to astrophysics, as it attempts to achieve these same goals on a much larger scale, studying the physics of entire universes and other large celestial bodies.
According to NASA, the goals of astrophysics are to better understand the origins of the universe, how planets and other celestial bodies are created and how the universe functions as a whole. Another primary goal of astrophysics is to discover whether or not life exists elsewhere in the universe. In addition, some astrophysicists dedicate their studies to the possibility of time travel and other such speculative questions. In fact, most of the work done by astrophysicists is based almost entirely in observational and theoretical physics, as there is almost no way to test any of their hypotheses.