Open dots depict dependence of the area of the largest sunspot within a year (GSO data) vs. the annual group (1874–1996) or international (1997–2013) sunspot numbers. Big filled dots denote the largest sunspot’s area for the days of reported NES observations during the period 1874–1918 (Yau & Stephenson 1988). The dashed and dotted lines depict the 100% (all spots above this line are visible) and 0% (detectability threshold) probability of observing a sunspot of the given area by an unaided eye, according to Schaefer (1993) and Vaquero & Vázquez (2009).
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