The evolution of the sunspots count is measured through the Sunspot Number.

Note that the Sunspot Number scale was revised on July 1st 2015.

the red area shows the Sunspot number excess for the Sun Southern hemisphere (13-months mean).

the blue area shows the Sunspot number excess for the Sun Northern hemisphere (13-months mean);

the red line represent the smoothed sunspot number, averaged over 13 months (6 months before, 6 months after and the current month)

Sunspot activity has been measured using the Wolf number

These images can then be added to our archive and used to calculate the Sun’s ‘Wolf number’, a crowd-sourced experiment to monitor solar activity.

Due to the fact that some sunspots may appear grouped, the "Wolf number" is used in the computation, which takes into account both the groups and the isolated sunspots.