A typical day for Professor David
The Wolf sunspot number
When the clouds are gone, the professor David can finally draw the Sunspots. Indeed the SIDC at the ROB, day after day observe, count and follow the evolution of the different Sunspots, thus producing a variable called the "Wolf Sunspot number". Our department has been providing the observatory with daily observations of the photospheric solar disk for thirty years. The observation consists in drawing the position of Sunspots and groups of spots on the cardboard. The Wolf Sunspot number is calculated by multiplying by ten the number of groups and adding to it the number of Sunspots. The Wolf number varies in a periodical way during a cycle of 11 years, ranging between 0 and 150 (or more) according to the intensity of the solar activity.

One can see here the scientist in action, who starts drawing the Sunspots and the plages on the cardboard. This work requires lots of patience and precision.
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