Sun offers Halloween 'trick or treat'

Sacramento Peak, NM (Oct. 31, 2002): The sun gave solar physicists a rare, perhaps unique, treat on Halloween with the nearly simultaneous eruption of flares on opposite edges of the sun. [...]

"This is called a sympathetic flare event," said Dr. Donald Neidig, ISOON project manager. Neidig specializes in solar flare observations and modeling at the NSO. "It happens when two active regions on the sun are energized and were on the verge of erupting anyway. If they are connected by magnetic flux tubes, the eruption of one can trigger the other within seconds. Or, a third, less powerful event, can trigger two more powerful active regions to go off at the same time."

"This is unique in that the two flares are on almost opposite sides of the solar disk, about 2.2 million km apart," Neidig said. "The two appeared at almost the same instant, which could indicate that something triggered the two."

The sun's diameter is 1.392 million km (870,000 miles). Traveling around the visible surface from one flare site to another is a distance of about 2.2 million km (1.4 million miles), too great for sound waves or even other effects to be the cause. (Most sympathetic events observed to date have been relatively close, separated by less than 700,000 km or so).

Dr. Alexei Pevtsov, a solar physicist at the NSO, estimates that even at a speed of more than 6,000 km/s (more than 13 million mph), a magnetic disturbance would take 5.8 minutes to reach from one side of the sun to the other. The Halloween flares erupted within a few seconds of each other. [...]