Example: Length of the Day

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This example applies the methods of Example 10 to model a periodic data set.

There are many cyclic phenomena in nature. The cycles of sunrise and sunset, and their seasonal changes, have been observed and recorded in all cultures, throughout history.

The U. S. Naval Observatory provides sunrise and sunset data for any location in the world during any year. (It also provides data for moonrise and moonset.) The length of the day is just the difference between the sunset and the sunrise times.

The following data gives the sunrise and sunset times on the first of the month for St. John, New Brunswick (45° 19' N, 65° 53' W) in 2000.