First, since we are studying history, we need to understand and define time. Why did humans develop the concept and measurement of time? Religion, agriculture, trade, astronomy, and navigation are all require some type of time keeping.

Most time systems today are categorized as either solar or lunar, based on whether the system follows on the sun or the moon to measure each passing year. For example, the Babylonians created a lunar system of 354 days, divided into twelve lunar months of either twenty-nine or thirty days in length. Lunar systems do, however, have their disadvantages. They eventually fall "out of whack" with the seasons and the stars. How valuable is a calendar if harvest time or planting time falls in a different month every year?

The Egyptians are thought to have been the first to create a calendar based on the sun. They noticed that Sirius, the "Dog Star," rose in the same place relative to the sun every 365 days. The Romans followed this system, adopting the 'Julian' calendar in 45 B.C.