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A Solar Show With Mixed Reviews

Kenneth Chang, The New York Times

Solar maximum is now. Indeed, the maximum — the peak of the 11-year sunspot cycle, when the sun erupts with solar flares and energetic bursts of electrons and protons — may have already passed.

Three X-class solar flares, the most powerful type, erupted June 10 and 11. The images are from NASA’s Solar Dynamics Observatory. CreditImage by NASA/SDO, via Goddard

As solar maximums go, this has been a tepid one, particularly when measured against some predictions that it would be ferocious; it has been called a “minimax.”

But neither does it rival a quiet period in the second half of the 1600s that coincided with the onset of the Little Ice Age, a prolonged chill in Europe.

“This cycle is not abnormally small,” said W. Dean Pesnell, the project scientist for NASA’s orbiting Solar Dynamics Observatory. Of the 24 solar cycles since the mid-1750s when people began keeping detailed counts of sunspots, “it looks like fifth smallest,” he continued. “It might be the fourth. It might be the sixth. It’s not going to be at the bottom.”

The sun erupted with several giant solar flares last month but has been mostly quiet the past two weeks.

“I think the general consensus is that we’ve passed the peak,” said C. Alex Young, a solar astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Md.

But he added that some of the biggest solar storms in history occurred on the downward side of the solar cycle, and even a weak cycle can generate ferocious outbursts.

“I think the expectation right now is we might see another burst of this activity five or six months from now,” Dr. Young said. “We might still have some big events.”

Perhaps more than anything else, the current maximum has taught solar scientists that they have a lot more to learn about the sun.

In 2006, at the end of the previous solar cycle, Mausumi Dikpati, a scientist at the National Center for Atmospheric Research in Boulder, Colo., undertook an ambitious endeavor — a computer model using the basic physics of the sun to forecast what would happen next. Her model made two main predictions: The cycle would start slowly, and it would be a big one, one-third to one-half stronger than the last one.

Her first prediction came to pass. The lull stretched for four more years, leading to some speculation that the sun was on the cusp of another Maunder Minimum, the sunspotless era of the 1600s.

(Although the Maunder Minimum coincided with the Little Ice Age, it is not known whether the intensity of a sunspot cycle could influence the earth’s climate. The difference in the amount of the earth-warming radiation coming from the sun between solar minimum and solar maximum is minuscule.)

But her second prediction was wrong.

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