How are sunspots formed? (Intermediate)

Why are sunspots created? What is the reason behind them?

Sunspots appear darker than the rest of the surface of the Sun because they are cooler. The center of a sunspot (called the umbra) has a temperature of around 3700 Kelvin while the surrounding photosphere has a temperature of 5800 Kelvin. Sunspots are also regions of strong magnetic fields (thousands times stronger than the Earth's field) and usually occur in pairs (one being a north pole and the other being a south pole).

Why certain regions on the Sun's surface are cooler than others is not well understood. One theory is that the strong magnetic fields in these spots inhibit convection below the surface. (Convection is the transfer of heat from a hot location to a cold one.)

This page was last updated June 28, 2015.

About the Author

Sabrina Stierwalt

Sabrina Stierwalt

Sabrina was a graduate student at Cornell until 2009 when she moved to Los Angeles to become a researcher at Caltech. She now studies galaxy mergers at the University of Virginia and the National Radio Astronomy Observatory in Charlottesville. You can also find her answering science questions in her weekly podcast as Everyday Einstein.

 Twitter: @galaxygirlguru

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