
Sunspot Numbers
Today, much more sophisticated measurements of solar activity are made routinely, but none has the link with the past that sunspot numbers have.  J.A. McKinnon
 International Sunspot Number  Brief Description
sunspot maximum and minimum 1610present; annual numbers 1700present; monthly numbers 1749present; daily values 1818present; and sunspot numbers by north and south hemisphere. The McNishLincoln sunspot prediction is also included.  Download data
Relative Sunspot Numbers  The collection of sunspot numbers provided here contains several kinds of tables  tables that give spot counts averaged over different time intervals. Professor M. Waldmeier, Director of the Swiss Federal Observatory in Zurich, Switzerland, published these observations in 1961 as a book entitled THE SUNSPOTACTIVITY IN THE YEARS 16101960 (Zurich Schulthess and Company AG) and updated more recently by the Royal Observatory of Belgium's Solar Influences Data Analysis Center.
The relative sunspot number is an index of the activity of the entire visible disk of the Sun. It is determined each day without reference to preceding days. Each isolated cluster of sunspots is termed a sunspot group, and it may consist of one or a large number of distinct spots whose size can range from 10 or more square degrees of the solar surface down to the limit of resolution (e.g., 1/25 square degree). The relative sunspot number is defined as R = K (10g + s), where g is the number of sunspot groups and s is the total number of distinct spots. The scale factor K (usually less than unity) depends on the observer and is intended to effect the conversion to the scale originated by Wolf.
The provisional daily Zurich relative sunspot numbers, Rz, were based upon observations made at Zurich and its two branch stations in Arosa and Locarno and communicated by M. Waldmeier of the Swiss Federal Observatory. Beginning January 1, 1981, the Zurich relative sunspot number program is replaced by the Solar Influences Data Analysis Center (formerly the Sunspot Index Data Center) (c/o Dr. R. Van der Linden, 3 av. Circulaire, B118 Bruxelles, Belgium). The determination of the provisional International Sunspot Numbers Ri results from a statistical treatment of the data originating from more than twentyfive observing stations. These stations constitute an international network, with the Locarno (Switzerland) station as the reference station, to guarantee continuity with the past Zurich series of Rz. The definitive International Sunspot Numbers Ri are evaluated by a similar method based on a network of observing stations selected for their high number of observations, their continuity during the whole year and an existing series of observations during the last years. Also taken into account is the stability of the K monthly factors with reference to the Locarno station. These relative sunspot numbers are now designated Ri (International) instead of Rz (Zurich).
The international sunspot number is produced by the Solar Influences Data Analysis Center (SIDC), World Data Center for the Sunspot Index, at the Royal Observatory of Belgium. NGDC kindly requests that you acknowledge the SIDC when using these data. Please refer to the SIDC site for additional information. The SIDC requests users of the data to credit: SIDC, RWC Belgium, World Data Center for the Sunspot Index, Royal Observatory of Belgium, `year(s)ofdata'.

Sunspot Numbers by Hemisphere.(19921996)  Download Data
 American Relative Sunspot Numbers  Download Data
Beginning with 1951, the observations collected by the Solar Division, AAVSO,
have been reduced according to a new procedure, such that only high quality
observations of experienced observers are combined into RA'. Observatory co
efficients for each of the 23 selected observers were recomputed on data for
19481950, years when there was a wide range of solar activity. Otherwise,
the procedure is that outlined in "Publication of the Astronomical Society of
the Pacific," "61," 13, 1949. The scale of the American numbers in 1951 will
differ from that of the reports for earlier years because of these changes,
and the new series is designated RA' rather than RA.

Ancient sunspot data 165 B.C. to 1684 A.D.

Group Sunspot Numbers (Doug Hoyt reevaluation) 16101995
 Descriptive text about data files  print before viewing data for data formats
 Files can be grouped into five categories  input, means, standard deviations, number of observations, and documentation files
 4a. Input files  alldata (raw daily input data for 463 observers) and filldata (raw data data with some missing days filled by linear interpolation)
 4b. Means files  dailyrg.dat, monthrg.dat and yearrg.dat
 4ba. dailyrg.dat  contains daily values of the Group Sunspot Numbers for 1610 to 1995
 4bb. monthrg.dat  contains monthly means of Rg with the number of days used to form the means and the standard deviation of the means
 4bc. yearrg.dat  contains yearly means of Rg with the number of days used to form the means and the standard deviation of the means
 4c. Standard deviation files  dailysd.dat, monthsd.dat and yearsd.dat
 4ca. dailysd.dat  contains daily standard deviations of the Group Sunspot Numbers for 1610 to 1995. These numbers represent the random errors in the daily means.
 4cb. monthsd.dat  contains the monthly means of daily standard deviations in dailysd.dat.
 4cc. yearsd.dat  contains the yearly means of monthly standard deviations in monthsd.dat.
 4d. Number of observations files  dailynum.dat, monthnum.dat and yearnum.dat
 4da. dailynum.dat  contains the daily number of observations per day used in forming the daily means.
 4db. monthnum.dat  contains the monthly average number of observations per day used in forming the daily means.
 4dc. yearnum.dat  contains the yearly average number of observations per day used in forming the daily means.
 4e. Documentation files  invent.dat, list1.dat, bibliogr.txt and alllevel.dat
 4ea. invent.dat  An inventory file listing the observer number, his observation year, and number of days of observations.
 4eb. list1.dat  A summary of the 463 observers used to reconstruct solar activity.
 4ec. bibliogr.txt  A bibliography listing the literature source of each observer used along with appropriate comments. Also listed are some observers identified but not used for one reason or another.
 4ed. alllevel.dat  A list of the calculated observer correction factors used to place the observer on the Royal Greenwich Observatory (RGO) scale. These factors make all the observers as selfconsistent as possible.
