Maintained by: Royal Observatory of Belgium. Associated with the Solar Influences Data analysis Center (SIDC), a FAGS service supported by UNESCO and ICSU.

Summary of Data Held: Zürich daily, monthly, monthly smoothed and yearly sunspot numbers, respectively since 1812, 1750 and 1700 (Rz) up to 1980; daily, monthly, monthly smoothed and yearly International Sunspot Numbers Ri computed from local Wolf numbers observed by a network of 45 (provisional data) to 100 (definitive data) observing stations, including Brussels, with Locarno (Associazione Specola Solare Ticinese) as reference station, since 1981; since 1992, North and South daily and monthly sunspot numbers Rn and Rs from a network of 25 to 45 stations (a subsystem of the former); individual original data on spots and groups from which Ri is calculated.

User Services: Monthly distribution of Ri, Rn and Rs to a network of more than 400 users, by fax or electronic mail and through the Sunspot Bulletin, with the predictions for the next 12 months. The International Sunspot Numbers files and predictions are also accessible through anonymous ftp (at present, jupiter.oma.be) and will be on WWW. A daily Prompt Photometric Sunspot Index (PPSI) is also provided. Information concerning the stability and dispersion of the individual data is furnished yearly to every station. The daily mean solar radio flux at 600 MHz is published in the Sunspot Bulletin.

Data Products, Publications, Catalogs: International sunspot numbers Ri since 1980 (continuation of the Zürich sunspot number Rz) and predictions of North and South sunspot numbers, PPSI. Publications are Sunspot Bulletin (monthly), SIDC News (4 to 6 times a year), some data in Part 1 of the Quarterly Bulletin of Solar Activity, and publications related to sunspot index analysis, and to positions and evolution of sunspot groups.