The period from 1645 to 1715 when scarcely any sunspots or aurorae were seen. E. W. Maunder (and, before him, G. F. W. Spörer) concluded that there had been a real decline in solar activity then. Further evidence for the Maunder minimum is provided by an increased carbon-14 content in tree rings during that period, since the cosmic rays that produce carbon-14 reach the Earth in greater numbers when the Sun's activity is low. There was also a lengthy cold spell on the Earth from 1550 to 1700, known as the Little Ice Age, which, roughly corresponds to a period including the Maunder minimum and the earlier Spörer minimum. This cold period could be explained by a decrease in solar output of about 1%. The existence of the minimum was confirmed in 1976 by the American solar physicist John Allen (‘Jack’) Eddy (1931–2009).
Subjects: Astronomy and Astrophysics — Meteorology and Climatology.