Bridging the gap between physics and astronomy textbooks, this book provides step-by-step physical and mathematical development of fundamental astrophysical processes underlying a wide range of phenomena in stellar, galactic, and extragalactic astronomy. The book has been written for upper-level undergraduates and beginning graduate students, and its strong pedagogy ensures solid mastery of each process and application. It contains over 150 tutorial figures, numerous examples of astronomical measurements, and 201 exercises. Topics covered include the Kepler-Newton problem, stellar structure, binary evolution, radiation processes, special relativity in astronomy, radio propagation in the interstellar medium, and gravitational lensing. Applications presented include Jeans length, Eddington luminosity, the cooling of the cosmic microwave background (CMB), the Sunyaev-Zeldovich effect, Doppler boosting in jets, and determinations of the Hubble constant. Table of Contents: Ch. 1: Kepler, Newton, and the mass function Ch. 2: Equilibrium in stars Ch. 3: Equations of state Ch. 4: Stellar structure and evolution Ch. 5: Thermal bremsstrahlung radiation Ch. 6: Blackbody radiation Ch. 7: Special theory of relativity in astronomy Ch. 8: Synchrotron radiation Ch. 9: Compton scattering Ch. 10: Hydrogen spin-flip radiation Ch. 11: Dispersion and Faraday rotation Ch. 12: Gravitational lensing