An Etymological Dictionary of Astronomy and Astrophysics

A quantity which gives the number of sunspots
at a given time. It is defined by the relationship R = k(10g + f), where R is the sunspot number, k is a constant depending on the observation conditions and the instrument used, g is the number of the groups and f is the number of individual spots that can be counted. Also called the
→ Wolf number and → relative sunspot number.

See also: → sunspot; → number.