Overview: Our ancestors' relationship with the heavens led to some of mankind's ancient discoveries and greatest creations. The ancient Greeks discovered Earth was round; the Polynesians used the sun and stars to navigate vast oceans in simple canoes; some think amazing structures like Stonehenge were designed to observe the sky. Now, Known Universe examines mankind's first observations of the cosmos to understand how they put us on the path to modern discovery. An alternate name of the episode: Star Gates