Today, amateur astronomers are monitoring a picturesque magnetic filament looping around the western limb of the sun. Jan Timmermans sends this picture from his backyard observatory in Valkenswaard, The Netherlands:
The portion of the filament seen in front of the sun looks dark, because it is cooler than the inferno below. But note how the filament glows in projection against the black space beyond the limb. The glow comes from plasma trapped inside the filament--not as bright as the surface of the sun, but definitely brighter than the void.
"The image clearly shows that the only difference between a 'dark' filament and a 'bright' prominence is where they are located: inside or outside the solar disk," notes Timmermans.
