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December 6: The Sinterklaas Eruption

     
  December 6: The Sinterklaas Eruption  
  The Sinterklaas Eruption  
 

 

Click on the above image for a movie of the event

 

 
 

Solar prominences are long bright magnetic structures observed extending outward from the Sun's surface. Typical prominences extend over thousands of kilometers and contain plasma at temperatures around 10,000 degrees. This temperature is considerably lower than the surrounding atmosphere (the corona). However, the density of a prominence can be up to 100 times greater than its surroundings, enhancing its brightness. When observed on the solar disk, prominences are (rather confusingly) called filaments. Filaments appear darker than the surrounding background solar disk due to their temperatures, and appear as long dark lines across the face of the Sun. Some more information on the nature and history of prominences can be found here.

Prominences can remain stable for quite a long time, supported by the magnetic field. However, many quiescent prominences do ultimately erupt in dramatic events. The eruptions are normally observed to move radially away from the solar surface. This happens because the magnetic fields initially supporting or constraining the structure have taken on a new configuration, often through a process known as magnetic reconnection, which releases energy. This energy can go into overcoming the strong gravitational pull of the sun and launching the field and the prominence material out into interplanetary space. Following the eruption, some material is often observed to fall back down towards the surface. This material can subsequently reform into another prominence.

Sinterklaas is a traditional Belgian holiday celebrating the arrival of St Nicholas on December 6. Because the above solar eruption occurred on this day three years ago (6th of December 2010), it is nicknamed the Sinterklaas Event. This particular event was extremely large, and material could be seen all the way to the edge of SWAPs large field of view (over one solar radii). The apparent twisting motions are created by material following the magnetic field lines surrounding the prominence. This large eruption was also tracked in several other instruments, such as LYRA on PROBA2, the AIA imagers on the SDO satellite and the coronagraph imagers on board the STEREO satellite.