Sunspot Cycle

A daily count of the number of sunspots visible on the Sun (the Wolf number or Zurich sunspot number) shows a periodic variation with maxima occuring (on average) every 11 years. During a solar sunspot minima, there may be no spots visible on the Sun for several days, and the number present during maxima varies with each cycle. The maxima of 1958 shows the highest sunspot activity on record.

From 1645-1715 there were very few sunspots, even during the maxima. This is known as the Maunder Minimum, and represents a period of solar inactvity that resulted in the ‘Little Ice Age’ on Earth.

The variation in sunspot numbers from 1800-2000, showing the 11 year solar cycle of sunspot maxima. A continous program of sunspot observations began in 1849.
Credit: National Geophysical Data Center (NGDC)

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