Astrophysics is a branch of astronomy that emphasizes theoretical understanding of celestial phenomena, while astronomy traditionally focused on observation and cataloging. The distinction between the two fields has blurred, with most modern astronomers also being considered astrophysicists due to their reliance on physics to explain cosmic events like the Big Bang and stellar behavior. Quantum physics plays a crucial role in astrophysics, helping to describe various phenomena, including star formation and supernovae. Historically, astronomy was limited to classical mechanics until advancements in relativity and quantum mechanics expanded the field significantly. Overall, both disciplines are interconnected, with astrophysics representing a more theoretical approach to understanding the universe.