This lecture aims to provide an overview of the physical concepts used in astrophysics to interpret observations from ground-based and space telescopes. It covers a wide range of concepts applied at various scales of time and space, taking students on a journey from our Solar System to the entire universe, including the formation and evolution of stars and galaxies. The instructor, Frédéric Courbin, a researcher at EPFL's astrophysics laboratory, emphasizes the connection between theoretical concepts and observations, making the course accessible to students with minimal prerequisites in physics.