Major change of data set on July 1st, 2015
Over the past 4 years a community effort has been carried out to revise entirely the historical sunspot number series. A good overview of the analyses and identified corrections is provided in the recent review paper:
Clette, F., Svalgaard, L., Vaquero, J.M., Cliver, E. W., "Revisiting the Sunspot Number. A 400-Year Perspective on the Solar Cycle", Space Science Reviews, Volume 186, Issue 1-4, pp. 35-103.
This is actually the first deep revision of the sunspot number since its creation By R. Wolf in 1849.
The new data series has been finalized and we are now preparing this important transition to the new data set, scheduled for July 1st. On this occasion, we don't only replace the original values of the sunspot number by new ones but we also change some important conventions and we also create a new set of data files. So, be prepared for the change!
More detailed information is available by clicking on the red warning message in the main page and will be attached to the files themselves in the "Data" section.