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The Maunder Minimum, also known as the "prolonged sunspot minimum", was a period around 1645 to 1715 during which became exceedingly rare. During the 28-year period 1672–1699 within the minimum, observations revealed fewer than 50 sunspots. This contrasts with the typical 40,000–50,000 sunspots seen in modern times over a similar timespan.
The Maunder Minimum was first noted by Gustav Spörer in publications in 1887 and 1889, work that was relayed to the Royal Astronomical Society in London, and then expanded on, by solar astronomers Edward Walter Maunder (1851–1928), and his wife Annie Russell Maunder (1868–1947), who also studied how sunspot latitudes changed with time. Two papers were published in Edward Maunder's name in 1890 and 1894, and he cited the two earlier papers written by Gustav Spörer. Because Annie Maunder had not received a university degree, restrictions at the time caused her contribution not to be publicly recognized. The term Maunder Minimum was popularised by John A. Eddy, who published a landmark paper in Science in 1976.
The Maunder Minimum occurred within the Little Ice Age, a long period () of lower-than-average European temperatures. The reduced solar activity may have contributed to the climatic cooling, although the cooling began before the solar minimum and its primary cause is believed to be volcanic activity.
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| 6 |
| 9 |
| 0 |
| 3 |
| Some sunspots (< 20) reported by Jan Heweliusz in Machina Coelestis |
| 0 |
| 1 huge sunspot observed by Giovanni Domenico Cassini |
During the Maunder Minimum enough sunspots were sighted that 11-year cycles could be determined from the count. The maxima occurred in 1676–1677, 1684, 1695, 1705 and 1718. Sunspot activity was then concentrated in the southern hemisphere of the Sun, except for the last cycle when the sunspots appeared in the northern hemisphere. According to Spörer's law, spots appear at high latitudes at the start of a cycle, subsequently moving to lower latitudes until they average about latitude 15° at solar maximum. The average then continues to drift lower to about 7° and after that, while spots of the old cycle fade, new cycle spots start appearing again at high latitudes. The visibility of these spots is also affected by the velocity of the Sun's surface rotation at various latitudes:
| 24.7 |
| 26.7 |
| 28.0 |
| 33.0 |
Visibility is somewhat affected by observations being done from the ecliptic. The ecliptic is inclined 7° from the plane of the Sun's equator (latitude 0°).
The correlation between low sunspot activity and cold winters in England has been analyzed using the longest existing surface temperature record, the Central England Temperature record. PDF Copy A potential explanation of this has been offered by observations by NASA's Solar Radiation and Climate Experiment, which suggest that solar ultraviolet light output is more variable over the course of the solar cycle than scientists had previously thought. A 2011 study found that low solar activity was linked to jet stream behavior, resulting in mild winters in some places (southern Europe and Canada/Greenland) and colder winters in others (northern Europe and the United States). In Europe, examples of very cold winters are 1683–84, 1694–95, and the winter of 1708–09. Hezekiah Niles' Weekly Register, Volume 15, Supplement, History of the Weather
Other historical sunspot minima have been detected either directly or by the analysis of the cosmogenic isotopes; these include the Spörer Minimum (1450–1540), and less markedly the Dalton Minimum (1790–1820). In a 2012 study, sunspot minima have been detected by analysis of carbon-14 in lake sediments. In total, there seem to have been 18 periods of sunspot minima in the last 8,000 years, and studies indicate that the Sun currently spends up to a quarter of its time in these minima.
A paper based on an analysis of a drawing by John Flamsteed suggests that the Sun's surface rotation slowed in the deep Maunder Minimum (1684).
During the Maunder Minimum had been observed seemingly normally, with a regular decadal-scale cycle. This is somewhat surprising because the later, and less deep, Dalton sunspot minimum is clearly seen in auroral occurrence frequency, at least at lower geomagnetic latitudes. PDF Copy Because geomagnetic latitude is an important factor in auroral occurrence, (lower-latitude aurorae requiring higher levels of solar-terrestrial activity) it becomes important to allow for population migration and other factors that may have influenced the number of reliable auroral observers at a given magnetic latitude for the earlier dates. Decadal-scale cycles during the Maunder Minimum can also be seen in the abundances of the beryllium-10 cosmogenic isotope (which unlike carbon-14 can be studied with annual resolution) PDF Copy but these appear to be in antiphase with any remnant sunspot activity. An explanation in terms of solar cycles in loss of solar magnetic flux was proposed in 2012. PDF Copy
The fundamental papers on the Maunder Minimum have been published in Case studies on the Spörer, Maunder and Dalton Minima.
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