sunspot is a time series of class "rts" and contains 289 observations.The Zurich sunspot numbers have been analyzed in almost all books on time series analysis as well as numerous papers. The data set, usually attributed to Rudolf Wolf, consists of means of daily relative numbers of sunspot sightings. The relative number for a day is given by k(f+10g) where g is the number of sunspot groups observed, f is the total number of spots within the groups and k is a scaling factor relating the observer and telescope to a baseline. The relative numbers are then averaged to give an annual figure. See Insenman (1983) for a discussion of the relative numbers. The figures are for the years 1700-1988.
Tong, H. (1990) Nonlinear Time Series: A Dynamical System Approach. Oxford University Press
Inzenman, A.J. (1983) J.R. Wolf and H.A. Wolfer: An historical note on the Zurich sunspot relative numbers. Journal of the Royal Statistical Society, A, 146, 311-318.
Waldmeir, M. (1961) The Sunspot Activity in the Years 1610-1960. Schulthess and Co.