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Breaking up time

Ancient Egyptians noticed that the Sun rose at different positions on the horizon depending on the season. In the warmer season when the crops grew, the Sun rose farther to the north. In the cooler season after the last harvest, the Sun rose farther to the south. They noted the position of the sunrise on a particular morning and tracked this position through the seasons. They found it took 365 sunrises before the Sun returned to the same position. Today people know that 365 days is the time it takes Earth to orbit around the Sun. We call that length of time a year. Technically, a year is 365 days, 5 hours, 48 minutes, and 46 seconds.

The ancient Egyptians also noticed a full moon occurred once every 29¹/₂ days—which is what we now called a month, from the Greek and Latin words for moon. The Egyptians chose to split up a month into groups of seven days. Historians theorize they could have...

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1. Introduction
2. Breaking up time
3. Swing time
4. A mess of times
5. Space-time: It's all relative
6. Atomic time
7. Experiment 1 - Pendulums: How do the length, weight, and swing angle of a pendulum affect its oscillation time?
8. Experiment 2 - Water Clock: Does the amount of water in a water clock affect its accuracy?
9. Design Your Own Experiment