What is the name of the period from 1645 to 1715 with very few sunspots?

The period from 1645 to 1715 with exceptionally few sunspots is called the Maunder Minimum. It was an unusually prolonged interval of low solar activity during which sunspots became extremely rare compared with normal solar cycles.

The period is named after British astronomers Edward Walter Maunder and Annie Russell Maunder, whose work helped reveal the pattern in historical observations. German astronomer Gustav Spörer had earlier identified evidence of the unusual interval. In 1976, astronomer John A. Eddy published an influential study that popularized the name and connected observations from several centuries.

The Maunder Minimum roughly overlapped the coldest part of the Little Ice Age, but that does not mean it single-handedly caused the era's colder climate. Modern research points especially to volcanic activity and other factors, while reduced solar activity may have made a smaller contribution. The Spörer Minimum occurred earlier, around 1460–1550, and the Dalton Minimum occurred later, around 1790–1830.