The Sunspot Relative Number (RSN) also known as Wolf Number, International Sunspot Number, or Zürich Number, is a quantity which measures the number of sunspots and groups of sunspots present on the surface of the sun.
The idea of computing sunspot numbers was originated by Rudolf Wolf in 1849 in Zürich, Switzerland and, thus, the procedure he initiated bears his name (or place). The combination of sunspots and their grouping is used because it compensates for variations in observing small sunspots.
This number has been collected and tabulated by researchers for around 300 years. They have found that sunspot activity is cyclical and reaches its maximum around every 9.5 to 11 years. This cycle was first noted by Heinrich Schwabe in 1843.
The Sunspot Relative Number (R), basically calculated from group number (G) and spot number (F) by a simple formula; R = K (10 G + F)
Where K is a constant determined by SIDC (Solar Influences Data Analysis Center), after an observatory sent the data routinely. Every observatory has different K. It depends on the average local atmosphere and environment parameters and instrumental parameters. A table of R, G and F has to be provided by an observatory
