The term 'Maunder Minimum' refers to a period of reduced sunspot activity between 1645 and 1715. This was first noticed by the English astronomer Edward Maunder in 1894. There was a similar period of reduced activity between 1450 and 1540, called the Spörer minimum, after the German scientist Gustav Spörer.
The Maunder minimum coincided with the coldest part of the “Little Ice Age” 1500–1850 in the Northern Hemisphere. During this period the Thames River in England froze over in winter, allowing 'Frost Fairs', and the Vikings abandoned Greenland. The relationship between solar activity and the climate on Earth is not yet established.