The text presents three lectures linking atomic physics and stellar astronomy, explaining how processes at the atomic and subatomic scale determine stellar interiors and observable properties. It examines theoretical estimates of interior temperature, ionization, radiation pressure, opacity, and the mass–luminosity relation, and discusses very dense stellar states. It surveys observational investigations including binary-star problems, spectral interpretation, nebulae and solar atmospheric phenomena, and notable variable stars. Finally it evaluates stellar evolution and age, treating pulsation and Cepheid distance indicators, the contraction hypothesis, and the role of subatomic (nuclear) energy and mass loss in powering and transforming stars.