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The Solar Cycle


The Sun's cycle of activity was discovered by an amateur astronomer, named Heinrich Schwabe, in Germany. Schwabe conducted observations of the Sun from 1826 to 1843 and determined that the Sun rotates on its axis once in 27 days. He also established that activity on the Sun increases and decreases over approximately an 11 year cycle. This theory was calculated on the occurrence of sunspots (dark areas caused by magnetic disturbances). Sunspots are cool areas that look like dark blemishes on the surface of the Sun. They form when magnetic field lines below the surface poke though the Sun's photosphere (a layer of the Sun's surface).

The Sun's activity cycle, called the "solar cycle" goes from minimum to maximum and back to minimum, as sunspots are absent, increase over time, and then decrease. The period of rise from minimum phase (when sunspots may be absent for several weeks) to maximum phase (when 20 or more groups may be present at one time) takes an average of four years. The decrease from maximum back to minimum occurs over the following seven years.

Schwabe also determined that the Sun's activity has terrestrial effects. The solar cycle causes variations in Earth's magnetic field. During the solar maximum there are numerous sunspots, solar flares (explosions on the surface of the Sun), and coronal mass ejections (charged particles thrown off the surface of the Sun). Energetic particles from these events, carried by the solar wind, affects our weather and cause disruption to communication, navigation, and power systems.


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   Webmaster: Diane K. Fisher
   JPL Official: Nancy J. Leon

   Last Updated:  01 / 04