Ficheiro:Sunspot Numbers.pngThis figure summarizes sunspot number observations. Since c. 1749, continuous monthly averages[dead link] of sunspot activity have been available and
Ficheiro:Sunspot Numbers German.pngsunspot numbers: A new solar activity reconstruction. Part 1.". Solar Physics 179: 189-219. Hoyt, D. V., and K. H. Schatten (1998b). "Group sunspot numbers:
Ficheiro:Sunspot Numbers-fr.svgsunspot numbers: A new solar activity reconstruction. Part 1.". Solar Physics 179: 189-219. Hoyt, D. V., and K. H. Schatten (1998b). "Group sunspot numbers: