Sinusoidal Graph Fitting Practice -- with Real Data!
The NOAA keeps close track of various kinds of weather data at a number of locations around the U.S. The NOAA station closest to me is in Chillicothe, Missouri. A graph of the hourly surface soil temperature in Chillicothe, starting on July 30, 2009, is shown below. (Source data here. Warning: this is a 5mb text file!)