The Sunspot Cycle Cycles have been around In the last few decades, we've started to understand the forces behind sunspots, but we've known for over a 150 years that sunspots appear in cycles. The average number of visible sunspots varies over time, increasing and decreasing on a regular cycle of between 9.5 to 11 years, on average about 10.8 years. An amateur astronomer named Heinrich Schwabe, was the first to note this cycle, in 1843. The part of the cycle with low sunspot activity is referred to as "solar minimum" while the portion of the cycle with high activity is known as "solar maximum." In fact they go around twice By studying the sun's magnetic field, modern astronomers have discovered that the cycle covers twenty-two years, with each eleven-year cycle of sunspots followed by a reversal of the direction of the Sun's magnetic field. According to Fisher, "the overall magnetic field structure changes in a way that is very interesting. It turns out that if the magnetic fields primarily point from west to east in the Northern Hemisphere (of the sun), they point from east to west in the Southern Hemisphere. In the next eleven-year cycle, the fields are reversed. So the cycle is really twenty-two years." Migration Sunspots appear mostly in the low latitudes near the solar equator. In fact they almost never appear closer than 5 or further than 40 degrees latitude, north or south. As each sunspot cycle progresses, the sunspots gradually start to appear closer and closer to the equator. The sunspot locations for the most recent 11-year cycle are shown in this "butterfly" diagram." The locations "migrated" toward the equator (0 latitude) from both hemispheres throughout this half of the cycle.   Do sunspots affect earth's climate? From 1645 to 1715, there was a drastically reduced number of sunspots. This period of reduced solar activity, which was first noticed by G. Spörer, was later investigated by E.W. Maunder, is now called the Maunder Minimum. That the same period of time was also unusually cold on Earth.  Similar periods of low solar activity seem to have occurred during the Spörer Minimum (1420-1530), the Wolf Minimum (1280-1340), and the Oort minimum (1010-1050). This succession of low-temperature periods is now called the "Little Ice Age," and the corresponding pattern of extreme sunspot minima has led to speculation that sunspot activity may affect the earth's climate.   ©Copyright 2001 Regents of the University of California.