The Sun supports a strong, changing magnetic field that varies year-to-year, reverses direction about every eleven years, and gives rise to many effects that are collectively called solar activity, including sunspots on the surface of the Sun, solar flares, and variations in the solar wind that carry material through the solar system and out into space. Such solar activity is believed to have played a large role in the formation and evolution of the solar system, and almost certainly still does.

Because of its high temperatures, all matter in the Sun is in the form of gas and plasma. This makes it possible for the Sun to rotate faster at its equator (about 25 days) than it does at higher latitudes (about 35 days near its poles).  

This differential rotation of the Sun’s latitudes causes its magnetic field lines to twist together, periodically causing magnetic field loops to erupt from the Sun’s surface, which in turn trigger the formation of sunspots and solar prominences.

The twisting action of the solar rotation gives rise to the solar dynamo and an 11-year solar cycle of magnetic activity with its corresponding sunspot activity. The magnetic field of the Sun varies over this 11-year cycle and reverses polarity at sunspot maximum. This results in a 22-year total cycle for the Sun’s magnetic field.

© Peter Dawkins