sunspot cycle

astronomy

Written by

The Information Architects of Encyclopaedia Britannica

Last updated

July 14, 2026

Quick Summary

The sunspot cycle is a roughly 11-year period of fluctuations in the number and size of sunspots and solar prominences. Sunspots are regions on the Sun's surface with extremely strong magnetic fields. These spots appear dark because they are cooler than the surrounding photosphere, about 3,000 K compared to 5,800 K.123

The cycle begins with new spots emerging at higher latitudes, gradually drifting towards the equator as the cycle progresses. The magnetic polarity of these spots reverses every 11 years, leading to a full magnetic cycle of 22 years. While the cycle is generally regular, there have been periods of significantly reduced activity, such as the Maunder minimum. The exact origin of the sunspot cycle is still being researched, but it is thought to be related to the Sun's differential rotation and magnetic field dynamics.23

Summary created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

4 Britannica Sources

Ask Britannica AI about this topic

Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.

telecommunications media
HF
…the peaks of the 11-year sunspot cycle, solar ultraviolet radiation produces the highest ionization densities. These sunspot peaks can last several days or months, depending on the persistence of sunspot visibility, producing a sporadic E layer that often can be used for multiple-skip communications by amateur radio operators at frequencies…
Read More
…the peaks of the 11-year sunspot cycle, solar ultraviolet radiation produces the highest ionization densities. These sunspot peaks can last several days or months, depending on the persistence of sunspot visibility, producing a sporadic E layer that often can be used for multiple-skip communications by amateur radio operators at frequencies…
Read More