Background: As summer fast approaches, the days are getting longer and the temperatures are getting warmer. But how do those two phenomena relate? Does more sunlight always mean warmer temperatures? Does less sunlight always mean cooler temperatures?

The graph shows a time series of hours of sunlight and average temperatures for Caribou, ME over the course of a year. The temperatures are daily averages from 1981 to 2010. Notice that this graph features two y axes. This allows you to compare two different sets of data that have the same x axis. Use the y axis on the right to read the hours of sunlight (solid line) and the y axis on the left to read the temperature (dashed line). 

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