A concise study surveys the evolution of Greek astronomy from observational and mythic beginnings through the development of geometric methods that made scientific modeling possible, culminating in Aristarchus of Samos’s heliocentric proposal. It outlines contributions of earlier thinkers who refined observational practice and theory, explains the mathematical approaches used to estimate the apparent sizes and distances of sun and moon, and examines arguments about the year and cyclical time. The volume situates these ideas within contemporary advances in Greek geometry, notes subsequent corrections to Aristarchus’s numerical results, and supplies bibliography and chronological material for further research.