Wolf-getal: verschil tussen versies

*{{en}} [http://cse.ssl.berkeley.edu/segwayed/lessons/sunspots/ The Exploratorium's Guide to Sunspots]

*{{en}} [http://sidc.oma.be/index.php3 RWC BelgiumBelgisch World Data Center forvoor thede Sunspot Indexzonnevlekindex]

*{{en}} [http://solarscience.msfc.nasa.gov/SunspotCycle.shtml NASA Solar Physics Sunspot Cycle page] and [http://solarscience.msfc.nasa.gov/greenwch/spot_num.txt TableTabel ofvan Sunspothet Numbersaantal zonnevlekken (txt)] byper monthmaand sincebijgehouden sinds 1749 CEn.Chr.