India, Nov. 22 -- Ancient Babylonians built watchtowers to study the sky, and used clay tablets to record the positions of ritually significant stars.

Their observations, the earliest dating to at least 2000 BCE, laid the foundation for early calendars.

By the 1st century BCE, the Ancient Egyptians were portraying the night sky in intricate detail. One surviving depiction consists of an astral disc affixed to the ceiling of the Hathor temple, built circa 50 BCE. The wheel-like structure features constellations associated, in startlingly familiar ways, with animals such as the ram, lion and bull. The wheel was detached and carted off, when Egypt was colonised by France, and is currently at the Louvre in Paris.

By the 3rd century BCE, th...