# Sunspot Number Determination

May 8th Fact-of-the-DaySome textbooks, magazine
articles, and websites falsely state that the Sunspot Number is
a count of the number of visible sunspots. Instead, it is a weighted average
of the number of visible groups-of-sunspots and sunspots. The actual formula
is R = k(10g + s); where R is the Sunspot Number, k is correction factor
near 1 that is applied to individual observatories to compensate for the
observation techniques and equipment they use, g is the number of visible
groups-of-sunspots, and s is the number of visible sunspots. Note that
the number of visible groups-of-sunspots is weighted ten times heavier
than the number visible sunspots. That formula was devised by Rudolph
Wolf and was published by him in 1848. He was the first director of the
Swiss Federal Observatory in Zurich and a physicist. *©2005 Martek,
International. All rights reserved.*

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