Maunder Minimum & Variable Sun
Solar Variations, Sunspot Activity Cycles, & Climate Changes
Aug 4, 2008
Using the newly invented telescope, Galileo discovered sunspots in 1610. A few decades later, sunspots became so rare that for about 75 years an observer could write a scientific paper describing a single sunspot. This time period corresponds to the coldest portion of the Little Ice Age.
The Maunder Minimum
Sunspots are dark spots on the Sun's photosphere. There is a well-known 11-year cycle in the amount of spot and other magnetic activity on the Sun. Studying old sunspot records, E. Walter Maunder noticed in 1894 that despite many people observing the Sun there were very few sunspots observed between about 1645 and 1715. Maunder's work was largely ignored until the mid-1970s when John A. Eddy confirmed that the Sun had 0.1% of the usual amount of sunspot activity during the Maunder minimum. Eddy also found other extended sunspot minima and a grand maximum in the past millennium.
For times after Galileo discovered sunspots, scientists can study written records to find the amount of sunspot activity. For pre-Galilean times, scientists use various indirect proxies. For the more distant past, the proxies become less accurate, but scientists have reconstructed the sunspot record using, for example geomagnetic activity and radioactive carbon in tree rings.
In addition to the Maunder minimum there was the Spoerer minimum from about 1450 to 1550, the Dalton minimum from about 1790 to 1820, and the Wolf minimum from about 1280 to 1350. There was also a medieval grand maximum from about 1000 to 1200. The last half of the twentieth century may be another grand maximum. During the extended minima, there are very few sunspots. During the grand maxima, the peaks in the 11 year sunspot cycle are higher than normal.
Solar Luminosity Variability
Satellite measurements show that during the sunspot minimum portion of the solar activity cycle the Sun's total energy output, its luminosity, is a very small amount lower than during sunspot maximum.
If this trend extends to the longer cycles, then during extended minima, such as the Maunder minimum, the Sun's luminosity should be lower than normal. During the grand maxima, the Sun's luminosity should be higher than normal. Unfortunately satellites cannot go back in time to accurately measure the Sun's luminosity during these periods.
Climate Change
Accurate climate records do not exist for most of the past 1,000 years. Scientists studying climate changes over this period must resort to indirect proxies and anecdotal evidence. Climate reconstructions show that the Maunder minimum occurred during the coldest portion of the Little Ice age. Other minima also correspond to cooler than normal periods during the past millennium. Conversely, the Medieval grand maximum was nearly as warm as the latter half of the twentieth century.
The Maunder minimum, other similar minima, and the Medieval grand maximum very likely strongly influenced both the Sun's luminosity and Earth's climate.
Further Reading
Eddy, J.A., "The Maunder Minimum" Science, v. 192, p. 1189-1192. 1976.
Foukal, P., Fröhlich, C. Spruit, H. and Wigley, T.M.L., "Variations in Solar Luminosity and Their Effect on Earth's Climate" Nature, v. 443, p. 161-166. 2006.
Golub, Leon and Pasachoff, Jay M. Nearest Star The Surprising Science of Our Sun. Harvard, 2001.
Maunder, E. Walter. "A Prolonged Sunspot Minimum" Knowledge, v. 17, p. 173-176. 1894
Maunder, E. Walter. "The Prolonged Sunspot Minimum, 1645-1715" Journal of the British Astronomical Society, v. 32, p. 140, 1922.
Soon, Willie Wei-Hock and Yaskell Steven H. The Maunder Minimum and the Variable Sun-Earth Connection. World Scientific. 2003.
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