This is a concise introduction to modern astrophysics for physicists, with a focus on galaxy dynamics and the discovery of dark matter halos in galaxies. Part I summarizes important discoveries in observational astronomy and astrophysics, in a manner accessible to those who are new to the topic. Building on this foundation, Part II describes the study of dark matter and provides more detail on galactic dynamics. Important physical concepts that form the basis of key astrophysical phenomena are explained, avoiding unnecessary technicalities and complex derivations. The approach is semi-empirical and emphasizes the importance of key measurements and observations in formulating fundamental theoretical questions and developing their solutions. Students are encouraged to develop a deep understanding of major discoveries and contemporary research topics, beyond the simple application of practical models and formulae, as a bridge to more advanced study in astrophysics.