The Maunder Minimum
Sunspot activity has been broadly increasing since the Maunder minimum period from 1645 to 1715, when there were very few sunspots. At a typical peak of the sunspot cycle, there may be as many as 1,000 spots a year, but during the Maunder minimum the number of spots dropped as low as one or two a year for a thirty-year period. This was also the peak of what has been called the Little Ice Age. This was a period of approximately 400 years, from the fifteenth to the nineteenth centuries, when the drop in temperature was so great that the winter mortality rate in Europe increased dramatically. In London, the river Thames froze over completely every winter. The edge of the Atlantic ice pack moved southward during the Maunder minimum and glaciers started expanding.
Sunspot Cycles
The general increase in the sun's activity has been consistent for more than 100 years, but it seems to have reached a peak in sunspot cycle 22 from 1986 to 1996. Sunspot cycle 23 began in 1996 and ended in 2008. The cycle was six months late and weaker than normal.
Cycle 24 was due to start in March 2008, but it is more than a year late already. As of July 2009, the first significant sunspot system has finally emerged. This is the longest period that the sun has been spotless for more than 100 years. Considering the maximum of this cycle is due in 2012, this might seem to suggest that the peak of the cycle may again be less than the recent average. Yet, generally this cycle is still predicted to be 30–40 percent more intense than the last one, although NASA has recently downgraded its projections for cycle 24 on the basis of the slow start to the cycle. The official prediction of the NOAA Space Weather Prediction Center is a peak of ninety sunspots in August 2012. There are also some predictions that delay in the cycle may cause the sun to suddenly burst into violent activity with another series of x-ray megaflares in the X-20+ range, or even cause another Carrington event.
The Maunder minimum was named after the astronomer Edward Maunder, who measured and photographed sunspots at the Greenwich Royal Observatory. It was his studies of this unusual period in history that led to his discovery of the important eleven-year sunspot cycle.
NASA's THEMIS satellite found that a 4,000-mile-thick layer of solar particles has gathered and is rapidly growing within the outermost part of the magnetosphere, a protective bubble created by Earth's magnetic field. This is causing a breach in the planet's magnetic defenses. This gap in the magnetosphere is more than four times the size of the Earth itself. This is not a problem at solar minimum, but at peak solar activity it could allow up to twenty times more plasma to impact Earth, making some of the worst solar storms in decades possible.
