sunspots

Sunspots are temporary phenomena on the Sun’s photosphere that appear darker than the surrounding regions because they are cooler. They are areas of concentrated magnetic flux that inhibit convection, leading to surface temperatures of roughly 3,000–4,500 K compared with the surrounding photosphere at about 5,800 K. Sunspots commonly occur in groups and have two parts: the dark core called the umbra and the lighter surrounding region called the penumbra.

Sunspots range in size from about 1,000 to tens of thousands of kilometers across. They form in complex magnetic field configurations and are indicators of the Sun’s magnetic activity. Sunspot activity follows an approximately 11-year cycle, with solar maximum featuring more sunspots and solar minimum with fewer. The magnetic polarity of sunspot groups also reverses each cycle, giving rise to a 22-year Hale cycle.

Historically, sunspots have been observed for centuries, with systematic records beginning in the early 17th century. Data sets such as the Greenwich Photoheliographic Results and the International Sunspot Number provide long-term indices of solar activity.

Sunspots are regions of intense magnetic activity and are often associated with other solar phenomena, including solar flares and coronal mass ejections from the same active regions. These events can affect space weather, satellite operations, radio communications, and power grids on Earth, though direct effects are typically indirect and occur during periods of high solar activity.

Locations tend to cluster at mid to low solar latitudes and migrate toward the equator as a cycle progresses, producing characteristic patterns known as the butterfly diagram. The solar dynamo, involving flows in the convection zone and magnetic field generation, explains sunspot formation and the cyclical nature of solar activity.