|The big filament is still there after all!|
|The 'mega-cool' filament is still visible in recent H-alpha pictures. It lasted for 3 solar rotations.|
|Nederlandstalige versie /Version française (traduit par PRAZZOLI Marc)||posted on April 14, 2005|
In the month February, an extremely large filament was visible on the solar disk. The black line in the left H-alpha picture, taken by the groundbased observatory in Catania, represents this plasma cloud. The next month, March 2005, the solar disk in H-alpha showed again the prominence. The prominence persisted and this month, April, it is once again clearly visible in the picture taken on April 13. The shape and the length has alternated. In the previous solar highlight, it was said that the prominence seemed to have disappeared as it did not show up in pictures taken on April 11.
A short note about the way prominences can disappear.
Prominences can disappear in two ways: a sudden disappearance and thermal disappearance. The first one is simply when the magnetic field lines holding the cloud break down and the plasma cloud is ejected into space resulting in a CME. The latter one is a thermal process in which the plasma is still present but has become transparant for H-alpha radiation. The prominence itself is heated resulting in more ionized atoms. The mores strongly ionized prominence cannot absorb or block the H-alpha radiation from beneath any more. The prominence as a plasma cloud is still present but has become transparant for H-alpha and does not show anymore as a black feature in H-alpha pictures. From such images, one cannot say if a disappearance is an eruption or a thermal process. In any case, this is not the issue here since most of the 'mega-cool' prominence is still there.