Wolf number

one of the numerical characteristics of solar activity; it is determined by the formula R = k(10g + f), where f is the number of spots on the solar disc and g is the number of groups uniting these spots. The coefficient k depends on many causes (conditions of visibility, the “personal equation” of the observer, the size of the telescope, and so forth). The Wolf numbers that have been published by the Zürich Observatory since 1849 have been accepted as the international system (k = 1). Despite their great inaccuracy, the Wolf numbers have the advantage over other characteristics of solar activity that their values have been determined for more than 200 years (since 1749). They are frequently used in comparing solar activity and many geophysical phenomena. R. Wolf introduced the Wolf numbers in the mid-19th century.