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The sun is surprisingly sleepy in comparison with other similar stars, which may mean that it will, at some point, enter a period of higher activity.

The varying activity and brightness of a star is driven by its magnetic field, which causes dark areas called starspots – or sunspots if they happen on the sun – as well as huge flares. Timo Reinhold at the Max Planck Institute for Solar System Research in Göttingen, Germany, and his colleagues compared measurements of this activity for 369 sun-like stars observed by the Kepler space telescope, along with the sun.

These stars all have similar temperatures, chemical compositions, ages, sizes and rotation periods. But despite all of these similarities, the researchers found that nearly all of these stars varied in brightness more than the sun.

“These stars are similar in every way we can measure to the sun, but many of them show variability up to five times higher than the sun, which was surprising,” says Reinhold. “One possible conclusion would be that there is some yet-unidentified quality of these stars that we don’t know that is different from the sun.”

In a larger sample of 2529 stars – the rotation periods of which we haven’t measured, but that are similar to the sun in every other way – most had similar variability to the sun. This could mean that the stars with rotation periods that we can measure may be more variable, for some reason.

Regardless, the fact that there are sun-like stars with much higher variability suggests it is possible that the sun could be in a temporarily calm phase now and its activity may ramp up in the future, says Reinhold. He says that while we can’t predict exactly when this could happen, it would lead to brighter auroras and potentially dangerous solar eruptions that could damage our electrical grids.

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