This book complements traditional astronomy texts by helping students apply core concepts to realistic problems using modern tools, especially Python, which is widely used in astronomical research. Rather than replacing foundational resources, it builds on them through hands-on, exploratory exercises designed for small-group work with instructor support. These exercises are open-ended and exploratory, encouraging deeper conceptual understanding. The material is presented in manageable sections to support active learning. The subject matter focuses on stars and planets and provides all figures as Python scripts at a separate website, enabling students to create interactive visualizations and animations that enhance their understanding of astronomical phenomena. Key features: An emphasis on key physical principles, and the notion of model building and testing in the physical sciences. A large number of examples and practice problems, including in-depth problems with multiple steps, and open-ended investigations. An emphasis on combining numerical calculations with analytical reasoning to solve astrophysical problems. Explicit instruction in how to understand and present quantitative information in graphical form, and supplementary example scripts for producing plots. Engagement with actual astronomical data and simulations.