ABSTRACT
Most people are not aware of the environmental rhythms that abound on Earth. As shown in Table 4.1, rhythmic oscillations in the environment range in period from a few femtoseconds (10-15 seconds) to tens of thousands of years. Some rhythms are human-made, such as 50 or 60 Hz alternated electric current and the 7-day week, while others are created by the Earth, the Moon, and the Sun. For example, ocean tides are caused primarily by the Moon’s gravitational attraction and secondarily by the Sun’s gravitational attraction.1 With a few exceptions, the interval between tides corresponds to half a “lunar day” — or 12 hours and 25 minutes (Figure 4.1).
