Sunspot Cycle

Eleven-year periodicity in the number of sunspots observed on the SunOur parent star. The structure of Sun's interior is the result of the hydrostatic equilibrium between gravity and the pressure of the gas. The interior consists of three shells: the core, radiative region, and convective region. Image source: http://eclipse99.nasa.gov/pages/SunActiv.html. The core is the hot, dense central region in which the. SunspotRegions on the Sun’s surface that appear dark because they are cooler than the surrounding photosphere, typically by ~1500-1800 K. Sunspots develop and persist for periods ranging from hours to months, and are carried around the surface of the Sun by its rotation. Sunspots travel in pairs (north and south maxima are associated with times of high solar activity (many flares and solar storms). During sunspot minima, there may be no spots visible on the Sun for several days. The number of sunspots present during the maxima varies with each cycle. The 1958 maxima showed the highest sunspot activity on record. There were very few sunspots from 1645-1715, even during the maxima. This interval is called the “Maunder Minimum,” and represented a period of solar inactivity that probably caused  the “Little Ice Age” on Earth.

Image source: http://www.theresilientearth.com/?q=content/little-ice-age-ii-sequel