At least one of a trio of huge sunspots that contributed to the record string of 10 major flares in late October and early November is about to rotate back into Earth’s view. And it remains active.
THE SPOT remains strong, and on Thursday it set off a good-sized flare and kicked up more space weather. Two other large sunspots trail the first are due back next week. All three have continued to generate space weather while on the far side of the sun, astronomers said.
Sunspot 484 will emerge into full view any day now. At 4:30 a.m. ET Thursday, it was the site of a moderate (M-class) flare and an associated coronal mass ejection, or CME, all detected because the radiation and matter leapt above the sun and became plainly visible.
The CME is a bubble of charged particles that expands outward into space. When aimed at Earth, a CME is one of the main components of space weather that fuels colorful sky aurora and can threaten satellites and power grids.
This storm is not aimed directly at Earth and is unlikely to have much effect.
But the eruption shows Sunspot 484 still has some kick. No one can say if it is capable of the sort of major (X-class) flares it created on its last trip across the face of the sun. While effects on the ground were minimal, two Japanese satellites were disabled and the operation of others was affected.
SEEING THROUGH THE SUN
Using a technique called helioseismic holography, astronomers look through the sun. They cannot see solar flares on the back side, but they can detect the sunspots and note any CMEs that expand beyond the solar disk.
“We have observed that active region 484 still appeared strong on Nov. 7,” said Paal Brekke, deputy project scientist for the sun-watching Solar and Heliospheric Observatory, or SOHO. “With LASCO we could see that it caused a few far-side halo CMEs while at the far side of the sun.”
Holographic maps from the SOHO spacecraft also reveal giant sunspots 486 and 488, which caused some of the other major flares recently. Space weather has continued to emanate from these regions, Brekke said, and if they don’t fade, these sunspots will slide back onto the visible disk next week.
Scientists and many in the public were surprised at the size of the sunspots that appeared in late October, and more so at the intensity and number of major solar flares — ten were ranked as X-class, including an X28 that is the most powerful ever recorded.
IS THE SUN OK?
The activity was all the more curious because the sun is a couple of years past the peak in its 11-year cycle of activity. Sunspots are, in general, fewer in number now than during the peak.
But historical data show that a slightly higher number of major flares occur after the solar cycle’s peak than during it. While the spate of 10 major flares in less than two weeks was unusual, it does not mean the sun is undergoing any fundamental change, astronomers say.
“Nothing’s wrong,” said David Hathaway, a solar physicist at NASA’s Marshall Space Flight Center. “These latest sunspots were whoppers,” Hathaway said, “but sunspot counts averaged over many weeks are still declining as predicted. We’re still on course for a solar minimum in 2006.”
During solar minimum, very few sunspots are expected, and flares would be infrequent.
Hathaway points out that accurate observations of solar flares, measured primarily by their X-ray output, is a recent effort, made possible only in the satellite era.
“It’s hard to be sure what’s normal and what’s not,” he said. “Astronomers have been observing X-rays from the sun for only 35 years — or three solar cycles. We can’t draw good statistical conclusions from so few data.”
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