The solar cycle is a rhythmic waxing and waning of the number of sunspots on the Sun. There are about 11 years between the times when the sunspot number is the greatest. We now know that the solar cycle is actually a magnetic cycle where the Sun’s magnetic poles reverse with a periodicity of approximately 22 years containing 2 sunspot cycles. Sunspots and active regions are seen on the surface of the Sun. Arching above them are coronal loops, magnetic field lines traced by the hot gas moving along the field. Many of the observed properties of the corona and solar wind come from the magnetic field. The heating of the material in the corona and the acceleration of the solar wind are probably caused by the interaction of small-scale magnetic elements. Solar flares and CMEs occur when magnetic fields in these loops are stressed beyond their limits. With the exception of the slow evolutionary changes in solar structure over the last 4.5 billion years, all solar variability is magnetic in origin.

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