How long is the solar cycle?

Since the invention of the telescope in the 1600s, observers have recorded variations in the numbers of dark spots, or sunspots, on the sun’s surface. Observations show that the sun exhibits a periodic change in the number of sunspots that normally follow a regular cycle with peaks 11 years apart.

NASA and the National Oceanic and Atmospheric Administration have continually monitored the sun from space since 1979. The solar cycle is coincident with an oscillation in solar energy output, with the sun’s output being slightly higher during periods with large numbers of sunspots.

Variations in solar output may affect climate on the time scales of decades to centuries. Between the years 1645 to 1715 the number of sunspots was dramatically lower than observed before or since. This period is known as the Maunder Minimum. It is hypothesized that the reduction in solar energy output during this period could have cooled the Earth. The historical record supplies some evidence supporting this hypothesis.

The period between about 1400 and 1850 is called the Little Ice Age in Europe, though it was not a true ice age. Around 1570 Europe was 2 to 4 degrees Farenheit cooler than it is today. The coldest portion of this period, accompanied by the greatest advance of mountain glaciers, occurred around 1750.

During a solar cycle, sunspots, solar flares and solar storms move from intense activity to relative calm and back again. Strong solar storms can disrupt communication, navigation systems and satellite instruments.

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