"Since a large amount of time in both astronomy and astrophysics is spent on theoretical and observational physics, a detailed explanation of both these branches is given here. This book attempts to decode the allure of space and to elucidate the extraordinary objects that are studied. The science behind both branches is explained while also giving its history and evolution into what it is today. This book will be helpful for those who are already acquainted with this field as well as newcomers."