Sunspots For centuries people have noted that the face of the sun is not constant or uniform in appearance, but that correlated with weather and other economically significant terrestrial phenomena. In 1848 Rudolf Wolfer proposed a rule that combined the number and size of these sunspots into a single index. Using archival records astronomers have applied wolfer's rule to determine sunspot activity back to the year 1700 today the sunspot index is measured by many astronomers and the worldwide distributioin of the data is coordinated by the sunspot index data Center at royal Observatory of Belgium http:/sidc.oma.be/html/sunspot.htmlSunspots For centuries people have noted that the face of the sun is not constant or uniform in appearance, but that correlated with weather and other economically significant terrestrial phenomena. In 1848, Rudolf Wolfer proposed a rule that combined the number and size of these sunspots into a single index. Using archival records, astronomers have applied Wolfer's rule to determine sunspot activity back to the year 1700. Today the sunspot index is measured by many astronomers and the worldwide distributioin of the data is coordinated by the Sunspot Index Data Center at Royal Observatory of Belgium. http://sidc.oma.be/html/sunspot.html