The number of sunspots observed on the sun has an 11-year cycle. It is easy to see the regularity of the sunspot cycle by examining observations taken over many years. Besides the 11-year cycle, there is an 80- to 90-year Gleisberg Cycle. From 1640 to 1710, an unusually low number of sunspots were observed. This period is known as the Maunder minimum. It coincided with a period of colder-than-average temperatures in northern Europe called the Little Ice Age.