Maunder Minimum

The Maunder minimum in a 400 year history of sunspot numbers

The Maunder Minimum (also known as the prolonged sunspot minimum) is the name used for the period roughly spanning 1645 to 1715 by John A. Eddy in a landmark 1976 paper published in Science titled "The Maunder Minimum",^[1] when sunspots became exceedingly rare, as noted by solar observers of the time. Astronomers before Eddy had also named the period after the solar astronomer Edward W. Maunder (1851–1928) who studied how sunspot latitudes changed with time.^[2] The periods he examined included the second half of the 17th century. Edward Maunder published two papers in 1890 and 1894, and he cited earlier papers written by Gustav Spörer. The Maunder Minimum's duration was derived from Spörer's work. Like the Dalton Minimum and Spörer Minimum, the Maunder Minimum coincided with a period of lower-than-average global temperatures.

During one 30-year period within the Maunder Minimum, astronomers observed only about 50 sunspots, as opposed to a more typical 40,000–50,000 spots in modern times.

Sunspot observations

The Maunder Minimum occurred between 1645 and 1715 when very few sunspots were observed. This was not due to a lack of observations; during the 17th century, Jean Dominique Cassini carried out a systematic program of solar observations at the Observatoire de Paris, thanks to the astronomers Jean Picard and Philippe de La Hire. Johannes Hevelius also performed observations, on his own. The total numbers of sunspots (but not Wolf numbers) in different years were as follows:

During the Maunder Minimum enough sunspots were sighted so that 11-year cycles could be extrapolated from the count. The maxima occurred in 1676, 1684, 1695, 1705 and 1716.

The 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, too.

According to Spörer's law, at the start of a cycle, spots appear at ever lower latitudes until they average at about lat. 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 rotation at various latitudes:

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°).

Little Ice Age

The Maunder Minimum coincided with the middle — and coldest part — of the Little Ice Age, during which Europe and North America, and perhaps much of the rest of the world, were subjected to bitterly cold winters. Whether there is a causal connection between low sunspot activity and cold winters is the subject of ongoing debate (e.g., see Global Warming).

Other observations

Solar activity events recorded in radiocarbon.

Graph showing proxies of solar activity, including changes in sunspot number and cosmogenic isotope production.

Some scientists hypothesize that the dense wood used in Stradivarius instruments was caused by slow tree growth during the cooler period. Instrument maker Antonio Stradivari was born a year before the start of the Maunder Minimum.^[3]

The lower solar activity during the Maunder Minimum also affected the amount of cosmic radiation reaching the Earth. The scale of changes resulting in the production of carbon-14 in one cycle is small (about 1 percent of medium abundance) and can be taken into account when radiocarbon dating is used to determine the age of archaeological artifacts.

Solar activity also affects the production of beryllium-10, and variations in that cosmogenic isotope are studied as a proxy for solar activity.

Other historical sunspot minima have been detected either directly or by the analysis of carbon-14 in tree rings; these include the Spörer Minimum (1450–1540), and less markedly the Dalton Minimum (1790–1820). 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.

One recently published paper, based on an analysis of a Flamsteed drawing, suggests that the Sun's rotation slowed in the deep Maunder minimum (1684).^[4]

During the Maunder Minimum auroras had been observed normally. Detailed analysis has been published by Wilfried Schröder^[5] and J. P. Legrand et al.^[6]

Curiously, the duration of the Maunder Minimum (1645-1715) coincides very closely with the reign of King Louis XIV of France (1643-1715), known as the Sun King.

The fundamental papers on the Maunder minimum (Eddy, Legrand, Gleissberg, Schröder, Landsberg et al.) have been published in Case studies on the Spörer, Maunder and Dalton Minima.^[7]

See also

• Spörer Minimum
• Solar minimum
• John A. Eddy, the astronomer who popularised the Maunder Minimum

References

Further reading

• Luterbach, J.; et al. (2001). "The Late Maunder Minimum (1675–1715) – A Key Period for Studying Decadal Scale Climatic Change in Europe". Climatic Change 49 (4): 441–462. doi:10.1023/A:1010667524422. 
• Willie Wei-Hock Soon; Yaskell, Steven H. (2003). The Maunder minimum and the variable sun-earth connection. River Edge, NJ: World Scientific. pp. 278. ISBN 9812382755. 
• What's wrong with the sun? (Nothing)