An Advance in Sid Meier's Civilization.
Perhaps the oldest of the sciences, astronomy originated as simple observation and recording of regular celestial movements. Ancient Greek students of astronomy understood that the Sun was the center of the solar system, made reasonable estimates for the sizes and distances of the Sun and the Moon, and made a close estimate of the size of the Earth.
Prerequisites: Mysticism and Mathematics.
Allows for: Navigation and Theory of Gravity.