THE SUNSPOT THAT WON’T EXPLODE: Measuring more than 150,000 km wide, sunspot AR2396 is one of the biggest sunspots of the current solar cycle. For the past week it has crossed the solar disk apparently poised to explode. Yet it has not. “It is a sleeping giant,” says Sergio Castillo, who photographed the behemoth from his backyard observatory in Corona, CA:

“AR2396 is huge, but dormant,” says Castillo. “There are very few flares erupting out of it.”

Castillo took the picture using a “Calcium K” filter tuned to the light of ionized calcium atoms in the sun’s lower atmosphere. Calcium K filters highlight the bright magnetic froth that sometimes forms around a sunspot’s dark core. AR2396 is very frothy, indeed.

Magnetic froth, however, does not herald an explosion. It merely means that the sunspot is photogenic.

from:    spaceweather.com