Editing Sunspot number (section)

{{Short description|Measure of sunspot activity}}
{{Misleading|date=August 2022}}
[[Image:Zurich sunspot number since 1750.png|thumb|350px|Wolf number since 1750.]]

The '''Wolf number''' (also known as the '''relative sunspot number''' or '''Zürich number''') is a quantity that measures the number of [[sunspots]] and groups of sunspots present on the surface of the Sun. Historically, it was only possible to detect [[Sunspot|sunspots]] on the far side of the Sun indirectly using [[helioseismology]]. Since 2006, NASA's [[STEREO]] spacecrafts allow their direct observation.