Since the beginning of civilization, our ancestors have been careful observers of the heavens. They knew that the Sun, the Moon and the stars have regular, repeating motions, but their patterns of motions are complicated. By 500 B.C., ancient astronomers knew that the Earth was round, and understood the cause of the phases of the Moon. More than 2000 years ago, the Greek astronomers could accurately determine the sizes of the Earth and Moon, and the distance to the Moon.

The ancient Greeks created a sophisticated model of the cosmos which can predict the times and directions of sunrise and sunset on any day of the year, at any place on Earth. They could also predict the positions of planets hundreds of years into the future. This system of cosmology was later integrated into the Christian theology that dominated European thinking for over 1000 years. It was not until that 16th century that an obscure clergyman developed a new cosmological theory that destroyed the philosophical foundation of European system of church and state.