|June 1: calculation of Ri|
|Every first day of the month, the provisional International Sunspot Number is calculated based on observations of sunspots sent to us by observers all over the world.|
|Nederlandstalige versie /Version française||posted on June 2, 2005|
The SIDC is the World Data Center for the International Sunspot Number. One of the tasks is to calculate and distribute on
the first of every month the provisional International daily and monthly mean Sunspot Number and the 12-months-ahead predictions.
Observers, amateurs as well as professional observatories provide us with their daily observed Wolfnumbers of the passed
month. The Wolfnumber equals by definition 10G+S, where G is the number of groups and S the number of sunspots
and was developed by Johann Rudolf Wolf.
The graph on the left pictures the provisional daily International Sunspot Number of May 2005 as they were calculated on June 1, 2005. The sunspot number is one of the indices to measure solar activity: if the Sun is spotted, we can expect more activity in the form of flares from it.