The Maunder Minimum, also called the "prolonged sunspot minimum," was a time from about 1645 to 1715 when sunspots became very rare. Between 1672 and 1699, during this period, scientists observed fewer than 50 sunspots. This is much lower than the typical 40,000 to 50,000 sunspots seen in modern times over a similar length of time.
The Maunder Minimum was first noticed by Gustav Spörer in papers published in 1887 and 1889. His work was shared with the Royal Astronomical Society in London and later expanded upon by solar astronomers Edward Walter Maunder and his wife, Annie Russell Maunder. They studied how the positions of sunspots changed over time. Two papers were published under Edward Maunder’s name in 1890 and 1894, and he referenced earlier work by Gustav Spörer. Because Annie Maunder did not have a university degree, her contributions were not publicly recognized at the time. The term "Maunder Minimum" became widely used after John A. Eddy published an important paper in Science in 1976.
The Maunder Minimum happened during the Little Ice Age, a long period from around 1300 to 1850 when European temperatures were lower than average. Reduced solar activity may have contributed to the cooling, but the cooling began before the solar minimum. Scientists believe the main cause of the cooling was volcanic activity.
Sunspot observations
The Maunder Minimum happened from 1645 to 1715, a time when very few sunspots were seen. This was not because people were not watching the Sun. During the 17th century, Giovanni Domenico Cassini conducted an organized study of the Sun at the Paris Observatory, with help from astronomers Jean Picard and Philippe de La Hire. Johannes Hevelius also made his own observations. Here are examples of sunspots recorded during each 10-year period (without Wolf numbers):
During the Maunder Minimum, enough sunspots were observed to identify 11-year cycles. The highest numbers of sunspots occurred in 1676–1677, 1684, 1695, 1705, and 1718. Most sunspots were found in the southern hemisphere of the Sun, except for the last cycle, when sunspots appeared in the northern hemisphere. According to Spörer's law, sunspots first appear at high latitudes at the start of a cycle. They then move to lower latitudes until they reach about 15° latitude at the cycle’s peak. After that, they drift to about 7° latitude. As sunspots from the old cycle fade, new sunspots begin to form again at high latitudes. The visibility of these sunspots is also influenced by how fast the Sun’s surface rotates at different latitudes:
The ability to see sunspots is slightly affected by observations being made from the ecliptic. The ecliptic is tilted 7° from the plane of the Sun’s equator (latitude 0°).
Eclipses during the Maunder Minimum
John A. Eddy wrote a very important paper about solar eclipses that happened during the Maunder Minimum. He studied reports from people who saw the eclipses in 1652, 1706, and 1715. He found that the solar corona was not very bright and had no clear shape during the Maunder Minimum. However, there were no pictures of these events available to him at the time. Some drawings of the events appeared in political cartoons, on coins, and on medals, but these were probably made by people who did not actually see the eclipses. Two prints of the 1706 event were made by witnesses, but they were created for commercial reasons and not by trained astronomers. In 2012, Markus Heinz from the Berlin State Library found two paintings of the 1706 eclipse. These paintings were made by Maria Clara Eimmart, a trained astronomer and observer. She was the daughter of the director of an observatory located on a part of the walls of Nuremberg Castle. The paintings matched detailed written descriptions of the event by Johann Philipp Wurzelbau in Nuremberg and by French mathematician Jean de Clapiès and astronomer François de Plantade, who observed the same event from Babote Tower in Montpellier. This supported Eddy’s conclusion that the solar corona was weak and had no clear structure during the Maunder Minimum. It also matched computer models of the F-corona, which has no visible K-corona shaped by magnetic fields, as seen in simulations for low magnetic activity. A full discussion of these observations and how the K-corona returned by the time of the 1715 eclipse is provided by Hayakawa et al. (2020).
Little Ice Age
The Maunder Minimum happened during the middle part of the Little Ice Age, a time when Europe and North America had colder than usual temperatures. Scientists are still studying whether the Maunder Minimum caused these colder temperatures. The best current idea is that volcanic activity caused the Little Ice Age. The Little Ice Age began before the Maunder Minimum started, and temperatures in the Northern Hemisphere during the Maunder Minimum were not much different from the previous 80 years. This suggests that lower solar activity was not the main reason for the Little Ice Age.
A connection between low sunspot activity and cold winters in England has been studied using the longest temperature record in the world, the Central England Temperature record. NASA's Solar Radiation and Climate Experiment has found that solar ultraviolet light changes more during the solar cycle than scientists previously thought. A 2011 study showed that low solar activity affected the jet stream, leading to mild winters in some areas (such as southern Europe and Canada/Greenland) and colder winters in others (like northern Europe and the United States). In Europe, very cold winters occurred during 1683–84, 1694–95, and 1708–09.
Other observations
Past solar activity can be studied using signs like carbon-14 and beryllium-10. These signs show that solar activity was lower during the Maunder Minimum. Changes in carbon-14 levels during one cycle are small, about one percent of normal levels, and are considered when using radiocarbon dating to find the age of ancient objects. Understanding the amounts of beryllium-10 and carbon-14 in places like ice sheets and tree rings has been helped by studies of solar and magnetic fields using historical data about geomagnetic storms. These studies connect the time between the end of old isotope data and the start of modern spacecraft data.
Other times of low sunspot activity, called sunspot minima, have been found by direct observations or by studying isotopes. These include the Spörer Minimum (1450–1540) and the Dalton Minimum (1790–1820). A 2012 study used carbon-14 in lake sediments to find sunspot minima. Studies show there have been about 18 sunspot minima in the last 8,000 years, and the Sun spends up to a quarter of its time in these minima.
A study based on a drawing by John Flamsteed suggests the Sun's surface rotation slowed during the deep Maunder Minimum (1684). During the Maunder Minimum, auroras were observed regularly with a cycle that repeated every 10 years. This is surprising because the less intense Dalton Minimum clearly affects aurora frequency, especially at lower geomagnetic latitudes. Since geomagnetic latitude influences aurora visibility, factors like population movement might affect how many people observed auroras in earlier times. Decadal cycles during the Maunder Minimum are also seen in beryllium-10 isotope levels, which can be studied yearly. These cycles appear opposite to any remaining sunspot activity. A 2012 study proposed an explanation involving solar cycles and the loss of magnetic flux.
Important studies about the Maunder Minimum are found in case studies on the Spörer, Maunder, and Dalton Minima.