A History of the Zurich and American Relative Sunspot Number Indices

Volume 31 number 1 (2003)

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Casper H. Hossfield

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Abstract

I trace the 133-year history of the Zurich Relative Sunspot Number index, R(z), from its beginning in 1848 through to 1981 when the index was terminated. I also trace the history of the American Relative Sunspot Number Index, R(A), from when it was first set to the Zurich scale in 1944 through to the present.