The Maunder Minimum, also called the "prolonged sunspot minimum," was a time from about 1645 to 1715 when sunspots became very rare. During the 28 years between 1672 and 1699, scientists saw fewer than 50 sunspots. This is much lower than the usual 40,000 to 50,000 sunspots observed in modern times over the same 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. Later, solar astronomers Edward Walter Maunder and his wife, Annie Russell Maunder, studied how sunspots changed in position over time. Edward Maunder published two papers in 1890 and 1894, and he credited Gustav Spörer’s earlier research. Annie Maunder’s work was not publicly acknowledged because she did not have a university degree at the time. The term "Maunder Minimum" became widely used after John A. Eddy wrote a major article 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 below average. Lower solar activity may have contributed to colder weather, but the cooling began before the Maunder Minimum. Scientists believe the main cause of the cooling was volcanic activity.

Sunspot observations

The Maunder Minimum happened between 1645 and 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 made careful and organized solar observations at the Paris Observatory, with help from astronomers Jean Picard and Philippe de La Hire. Johannes Hevelius also made his own observations. Here are the total sunspots recorded, for example, in each 10-year period (without using Wolf numbers):

During the Maunder Minimum, enough sunspots were seen to identify 11-year cycles based on their numbers. The highest activity occurred in 1676–1677, 1684, 1695, 1705, and 1718. Sunspots were mostly found in the southern hemisphere of the Sun, except during the last cycle, when they appeared in the northern hemisphere. According to Spörer's law, sunspots begin at high latitudes at the start of a cycle, then move to lower latitudes until they reach about 15° latitude at the cycle’s peak. After that, they continue to move to lower latitudes, reaching about 7°. As sunspots from the old cycle fade, new sunspots from the next cycle begin to appear again at high latitudes. The visibility of these sunspots is also influenced by how fast the Sun’s surface rotates at different latitudes:

Visibility 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 an 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 weak and not organized during the Maunder Minimum. However, he did not have pictures or drawings of these events. Some images of the eclipses appeared in political cartoons, coins, and medals, but these were probably not made by people who actually saw the events. Two drawings of the 1706 eclipse were made by witnesses, but they were created for commercial purposes and not by trained astronomers. In 2012, Markus Heinz from the Berlin State Library found two paintings of the 1706 eclipse. These paintings had been thought lost but were known to exist. The paintings were created by Maria Clara Eimmart, a trained and skilled astronomer and observer. She was the daughter of the director of an observatory located on a bastion of the walls of Nuremberg Castle. The paintings matched detailed written descriptions of the event by Johann Philipp Wurzelbau, who lived in Nuremberg, and by French mathematician and cartographer Jean de Clapiès and astronomer François de Plantade, who observed the same event from the Babote Tower in Montpellier. This supported Eddy’s conclusion that the corona was weak and structureless during the Maunder Minimum. It also agreed with models showing a structureless F-corona, with no detected K-corona, which is shaped by magnetic fields, as predicted for low coronal magnetic flux. A complete discussion of these observations and how the K-corona had returned by the time of the 1715 eclipse is provided by Hayakawa et al. (2020).

Little Ice Age

The Maunder Minimum happened around the same time as the middle part of the Little Ice Age, when Europe and North America had colder than usual temperatures. Scientists are still studying whether these events are connected. The best idea so far for why the Little Ice Age happened is that it was caused by volcanic activity. 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 available, called the Central England Temperature record. NASA's Solar Radiation and Climate Experiment observed that the sun's ultraviolet light output changes more during the solar cycle than scientists previously believed. A 2011 study found that low solar activity influenced the jet stream, causing mild winters in some areas (such as southern Europe and Canada/Greenland) and colder winters in others (such as northern Europe and the United States). In Europe, very cold winters occurred during 1683–84, 1694–95, and the winter of 1708–09.

Other observations

Scientists use certain clues, like carbon-14 and beryllium-10, to study past solar activity. These clues 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 must be considered when using radiocarbon dating to find the age of ancient objects. Understanding records of beryllium-10 and carbon-14 levels in places like ice sheets and tree rings has been helped by studies of solar and space magnetic fields based on 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, like the Spörer Minimum (1450–1540) and the Dalton Minimum (1790–1820), have been found by studying sunspots directly or by analyzing isotope levels. A 2012 study found sunspot minima by studying carbon-14 in lake sediments. Over the last 8,000 years, there have been about 18 periods of low sunspot activity, and research suggests the Sun spends up to a quarter of its time in these minima.

A paper 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 (northern lights) were observed regularly, following a 10-year cycle. This is surprising because the less severe Dalton Minimum clearly shows fewer auroras at lower geomagnetic latitudes. Since geomagnetic latitude affects aurora visibility (lower-latitude auroras require stronger solar activity), it is important to consider factors like population movement that might have changed the number of people observing auroras in earlier times. Decadal cycles during the Maunder Minimum also appear in beryllium-10 isotope levels (which can be studied yearly) but seem opposite to any remaining sunspot activity. A 2012 explanation linked these patterns to changes in the Sun’s magnetic field.

Key research on the Maunder Minimum is included in studies comparing the Spörer, Maunder, and Dalton Minima.