Solar cycle

The roughly 11-year variation in the Sun’s magnetic activity, marked by changing sunspot numbers and reversals of its global magnetic field.

Solar dynamo: The process by which motions of electrically conducting solar plasma generate and maintain the Sun’s magnetic field. Differential rotation and convection drive the magnetic-field changes that structure the cycle.
Sunspot: A relatively cool, dark region on the solar photosphere associated with concentrated magnetic fields. Sunspots are the most familiar visible markers used to track the cycle.
Space weather: Conditions in space shaped by solar activity and its interactions with Earth’s magnetosphere and atmosphere. The cycle modulates the frequency of solar disturbances that can affect Earth.
Samuel Heinrich Schwabe: A German astronomer who identified the roughly decadal variation in sunspot counts through observations from 1826 to 1843. His patient observations revealed the recurring pattern now called the solar cycle.
Solar cycle prediction: The forecasting of the timing and strength of future solar activity cycles. Forecasts remain uncertain because the Sun’s internal magnetic evolution is only partly observed.
Differential rotation: Rotation in which different parts of a body spin at different angular velocities. The Sun’s latitude-dependent rotation stretches magnetic fields as a cycle begins.
Butterfly diagram: A plot showing how sunspot emergence shifts from higher to lower solar latitudes over a cycle. Its paired wings show the cycle’s characteristic equatorward drift of sunspot belts.
Geomagnetic storm: A major disturbance of Earth’s magnetosphere caused by energy transfer from the solar wind. Storm risk rises when cycle-related eruptions and fast solar wind streams reach Earth.
Rudolf Wolf: A Swiss astronomer who developed a standardized sunspot number and reconstructed historical solar activity. His counting method made cycle timing comparable across observers and decades.
Solar dynamo theory: The theoretical study of how fluid motions and magnetic fields generate and sustain stellar magnetism. Competing dynamo models seek to explain the cycle’s variability and irregular timing.

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