Scientists started to make records of sunspot activity in the mid 18th century, and by the mid 19th it was discovered that the number of spots (which are lower-temperature entry-and-exit points for magnetic-flux=lines penetrating the Sun's surface) varies on a very regular cycle of approximately 11.1 years.

The reason for the oscillation is unknown.

We are currently in the 25th recorded cycle.

The magnetic poles of the sun flip with each cycle, so it may be more accurately described as a 22.2 year cycle.

The cycles are now being carefully studied - because the intensity of solar flares and magnetic events on the Sun, which are also linked to the cycle, have been found to strongly affect electronic equipment in Earth orbit. As well as influencing weather events and (to an unknown extent) biological systems etc.

Further reading : The calm before the storms Science, Vol. 364, Issue 6443, pp. 818-821, May 2019.

Also see Solar flaresplugin-autotooltip__plain plugin-autotooltip_bigSolar flares

The first solar flare to be formally documented was recorded by astronomer Richard Carrington, who observed a 'white light' flare in September 1859 - projecting the image produced by an optical telescope, without filters. See: Wikipedia

However, the mechanisms producing the white light flares and their emissions have yet to be fully explained. This extract is from a 2016 paper from the and Solar 'dynamo'plugin-autotooltip__plain plugin-autotooltip_bigSolar 'dynamo'

"Explaining the origin of the Sun’s magnetic field is the fundamental problem of solar magnetohydrodynamics (MHD). This dynamic magnetic field is responsible for all solar magnetic phenomena, such as solar flares, coronal mass ejections and the solar wind, and also heats the solar corona to extremely high temperatures. These phenomena all have important terrestrial consequences, causing severe magnetic storms and major disruption to satellites, as well as having a possible impac…

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