Fig. 1From: A review of the SCOSTEP’s 5-year scientific program VarSITI—Variability of the Sun and Its Terrestrial ImpactInstrumental sunspot observations: group sunspot number (Hoyt and Schatten 1998)—blue line and international sunspot number (Clette et al. 2007)—red line. The shaded area indicates the “space era” which started with the launching of the first artificial satellites of the Earth for in situ measurements in the outer spaceBack to article page