What is the term for the 11-year sunspot cycle named after a German astronomer?

The approximately 11-year sunspot cycle named after German astronomer Heinrich Schwabe is the Schwabe cycle.

The Schwabe cycle describes the recurring rise and fall in the number of sunspots and in broader solar activity. During solar minimum, relatively few sunspots appear. Activity increases toward solar maximum, when sunspots, solar flares, coronal loops, and solar eruptions become more common. The cycle’s average length is about 11 years, although individual cycles vary.

Samuel Heinrich Schwabe, a German amateur astronomer, spent decades observing and drawing sunspots. In 1843, after 17 years of observations, he reported a periodic pattern in their numbers. His work helped establish the solar cycle, which was later quantified and numbered by astronomers including Rudolf Wolf.

The Schwabe cycle is sometimes called the sunspot cycle or solar cycle. It should not be confused with the Hale cycle: the Sun’s magnetic polarity reverses during each Schwabe cycle, so the magnetic pattern returns to its original orientation only after roughly two cycles, or about 22 years. The Gleissberg cycle is a longer-term modulation of solar activity.