Hi Oliva,

We are currently at the end of solar cycle 23 and beginning of 24. So multiply this by 11 years, it goes back to 253 year. We started having record of sunspot numbers since before year 1800. The eleven-year cycle was discovered in 1834 by the German astronomer Heinrich Schwabe. Actually the cyclic activity of the Sun is not exactly 11 years, which is an average number. It can be as short as 9 year and as long as 14 years.

The solar cycle is not completely understood. It is to believed to be caused by "the solar dynamo", which is related to the solar rotation and other motions in the solar body and their interactions with the solar plasma (the hot and ionized gas of the Sun). It is very complex and is still a major effort of solar physicists.

Yan