Astronomy is the study of the universe beyond the Earth. It is both a natural science, which studies the physical universe, and a social science, which studies the way people have interpreted the universe. Astronomy is one of the oldest sciences. It began with the ancient Greeks, who developed a model of the universe that included the Earth at the center. This model was later disproven by the work of Copernicus and Galileo. However, the basic principles of astronomy are still based on the work of the Greeks.