Wolf's Number
The Wolf number (also known as the International sunspot number or Zurich number) is a quantity that measures the number and size of of sunspots.
The idea of computing sunspot numbers was devised by Rudolf Wolf in 1848 in Zurich, Switzerland, and thus the procedure is named after him or the place. The combination of sunspots and groups is used because it compensates for the variations in observing small sunspots.
This number has been used by researchers for about 300 years. They have found that solar activity is cyclical, peaking around every 9.5 to 11 years (note: corresponding to SIDC data Archived 2017-08-03 at the Wayback Machine. for the last 300 years and running the Fourier transform, a duration of 10.4883 years is obtained for the cycle This cycle was discovered by Heinrich Schwabe in 1843.)
The Wolf number is computed as a daily index of solar activity:
R=k(10g+s){displaystyle R=k(10g+s),!}
where:
- R is the number of the relative sunspot,
- s is the number of individual stains,
- g is the number of groups of the sunspot, and
- k is a factor that varies with the situation and instrumentation (also known as observatory factor).