The sun is thought to have reached the lowest point in its activity in December 2008, but the new solar cycle has gotten off to a slow start. This week, however, two active regions (bright regions in upper-left corner) – whose knotty magnetic fields often coincide with eruptions and flares – appeared on the far side of the sun. One of NASA’s twin STEREO probes snapped this image on Thursday (Image: NASA/Goddard Space Flight Center)

The sun’s new solar cycle, which is thought to have begun in December 2008, will be the weakest since 1928. That is the nearly unanimous prediction of a panel of international experts, some of whom maintain that the sun will be more active than normal.

But even a mildly active sun could still generate its fair share of extreme storms that could knock out power grids and space satellites.

Solar activity waxes and wanes every 11 years. Cycles can vary widely in intensity, and there is no foolproof way to predict how the sun will behave in any given cycle.


In 2007, an international panel of 12 experts split evenly over whether the coming cycle of activity, dubbed Cycle 24, would be stronger or weaker than average.

The group did agree the sun would probably hit the lowest point in its activity in March 2008 before ramping up to a new cycle that would reach its maximum in late 2011 or mid-2012.

But the sun did not bear out those predictions. Instead, it entered an unexpectedly long lull in activity with few new sunspots. It is thought to have reached its minimum in December 2008, and now seems to be slowly waking up. One such sign is two new active regions captured this week by the ultraviolet camera on one of NASA’s twin STEREO probes (see image).

‘Ready to burst out’

“There’s a lot of indicators that Cycle 24 is ready to burst out,” panel chair Doug Biesecker of the National Oceanic and Atmospheric Administration Space Weather Prediction Center in Boulder, Colorado, told reporters on Friday.

The panel now expects the sun’s activity will peak about a year late, in May 2013, when it will boast an average of 90 sunspots per day. That is below average for solar cycles, making the coming peak the weakest since 1928, when an average of 78 sunspots was seen daily.

Sunspots are Earth-sized blotches that coincide with knotty magnetic fields. They are a common measure of solar activity – the higher the number of sunspots, the higher the probability of a major storm that could wreak havoc on Earth (see Space storm alert: 90 seconds from catastrophe).

Not unanimous

A lower number of sunspots could mean space weather will be relatively mild in the coming years. But Beisecker cautions it may be too early to call. “As hard as it is to predict sunspot number, it’s even harder to predict the actual level of solar activity that responds to those sunspots,” he told reporters. If there are fewer storms, they could still be just as intense, he said.

But not everyone on the panel expects the coming cycle to be weaker than average. “The panel consensus is not my individual opinion,” says panel member Mausumi Dikpati of the High Altitude Observatory in Boulder, Colorado.

Dikpati and her colleagues have developed a solar model that predicts a bumper crop of sunspots and a cycle that is 30% to 50% stronger than the previous cycle, Cycle 23.

Because it is still early in the new cycle, it is too soon to say whether the sun will bear out this prediction, Dikpati says. “It’s still in a quiet period,” she told New Scientist. “As soon as it takes off it could be a completely different story.”