Hi All, I found this passage at the end of the wiki page on sun spot obseravtions "Sunspot research was dormant for much of the 17th and early 18th centuries because of the Maunder Minimum, during which no sunspots were visible for some years; but after the resumption of sunspot activity, Heinrich Schwabe in 1843 reported a periodic change in the number of sunspots. Since 1991, the Royal Observatory of Belgium keeps track of sunspots as the World data center for the Sunspot Index." It seems most sunspot activity during the time (17th and early 18th century) was mostly derived or extrapolated and not directly observed. Most data prior to the 17th century was derived from carbon dating and tree rings. Erik