Spectacular prominence eruptions on January 21 and 22, 2004

The first prominence, situated at the left (east) of the central meridian, erupted on 21 January. This led to a nice view in EIT 195 (see figure and movie underneath). At this time we already could predict the outburst of a second prominence, situated on the right edge (west limb) of the Sun. The small turbulent motions inside the prominence revealed the future activity.

What is a prominence? ... and a filament?

Prominences are amazing objects. They are located in the corona, but are much cooler and have densities a thousand times greater than coronal values. Prominences have a quite stable structure and can live for several weeks or months. In fact prominences and filaments are the same thing. When we see them in profile against the dark sky they look like giant bright arches above the surface of the Sun, quite spectacular if you ask me. Viewed on the solar disk they appear as long dark ribbons called filaments. They are best observed in H-alpha. These dense plasma clouds are held together by magnetic field lines connecting regions of opposite polarity. Therefore a prominence is never located above a sunspot itself, but in between them.

H-alpha image of the Sun on 20/1/2004, before the eruptions.
(1) The filament which erupted on 21/1 lead to post-flare loops.
(2) The large prominence which erupted on 22/1.
(Image credit: Big Bear Solar Observatory.)

EIT 195 movie of the Sun from 16 till 22 January 2004   

What causes a prominence to erupt?

A prominence can die a gentle death, or erupt drastically blowing cool gas into space. During the lifetime of a prominence the magnetic field lines holding the plasma are twisted around each other. The magnetic field will become stronger and this causes the "arch" to grow higher and higher. At a certain point the magnetic field lines are so stretched that it can't hold the plasma anymore. At this stage an amount of cool gas from the prominence will be blown into space leading to a coronal mass ejection (CME).

Any harm for us humans?

When the prominence is directed towards the Earth at the time of eruption, the dense plasma cloud blown into space is directed to the Earth. After 2-4 days this cloud will bump onto the magnetosphere of the Earth and disturb it. The fist filament eruption was directed to us and could therefore trigger a geomagnetic storm on 23/1 or later. Keep an eye on our presto!

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