Why sunspots occur

Scientists measure them by comparing them to the sun's visible area that is, the half of the sun that we can see from Earth. The biggest recorded sunspot in the last century occurred in It covered 6, millionths of the sun's visible area -- roughly 18 times the Earth's surface area [source: European Space Agency ].

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Coming Soon: More travel opportunities with Astronomy. Sign up. Table of Contents Subscribe Digital Editons. Our Sun isn't the only star with spots. In recent years, astronomers have been able to detect "starspots" - "sunspots" on other stars.

Skip to main content. More about Sunspots. In this image, you can see an active region on the sun with dark sunspots.

The magnetic field lines near sunspots often tangle, cross, and reorganize. This can cause a sudden explosion of energy called a solar flare.

Solar flares release a lot of radiation into space. If a solar flare is very intense, the radiation it releases can interfere with our radio communications here on Earth. A loop of solar material, a coronal mass ejection CME , can also be seen rising up off the right limb of the Sun. Solar flares are sometimes accompanied by a coronal mass ejection CME for short.

CMEs are huge bubbles of radiation and particles from the Sun.