The "Wolf number" is a measure used in solar physics to quantify the number of sunspots on the surface of the Sun. It helps scientists understand solar activity and its effects on space weather. The Wolf number is calculated using a formula that considers both the number of sunspots and the area they cover. This measurement is named after the Swiss astronomer Rudolf Wolf, who developed the system in the 19th century. By tracking the Wolf number over time, researchers can study solar cycles and their potential impact on Earth, including effects on communication systems and satellite operations.