itions of the planets and stars. Time may also have been used by physicians. For example, a physician would want to know when a newborn might be expected. Finally, the development of early civilization corresponded to a shift in technology. Early humans went from nomadic tribes of hunter-gatherers to more stable agricultural societies. The planting and harvesting of crops certainly required that humans understand time.
Of course, the first actual timekeeping device consisted of the sun-dial. In its simplest form, the day's progress could be monitored by following the movement of the sun's shadow cast by a vertical rod, or gnonom. Evidence of sun-dials dates as far back as the beginning of the second millennium B.C. Certainly, calendrical gnomons were being used in Greece during the fifth century B.C. The earliest datable surviving Greek sun-dial, however, comes from the third century B.C.
The widespread use of the sun-dial marked a human cultural transition. People began the
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