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Sunspot Number Determination

May 8th Fact-of-the-Day

Some 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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