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prominences are "cool"


It’s true! Prominences have temperatures between 5,000 oC and 8,000 oC. In an region where the average temperature is around 1,000,000 oC, that's positively chilly. Prominences are dense clouds of plasma which just hang around above the chromosphere in the hot, thin corona.


When a prominence is seen against the disk of the Sun, it looks dark and is called a filament


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H-alpha image of a prominence from Tenerife Observatory

H-alpha image of a prominence from Big Bear Solar Observatory


H-alpha prominence

When the prominence is seen off the edge of the Sun, as in this picture, it appears bright


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Image from the High Altitude Observatory


Apparently not everything that goes up must come down!


HammockA prominence is a relatively cold, dense structure suspended in a thinner and very much hotter environment. This goes against our normal experience. Hot material rises, cold material sinks, so something must be holding these prominences up.


What’s more, if you put a cold object next to a very hot object, the cold one usually heats up very quickly. It’s as if the prominence is taking a rest in a cool hammock above a roaring fire, without even getting warm!


There’s good evidence that the Sun’s magnetic field is the key to all this. Here’s an experiment you can try yourself. It shows the principle behind one possible explanation for pominences.


Have a go and find out for yourself...


Take a ring magnet and attach it to a rod and base as shown in the diagram (this represents the solar surface).


Now place a second ring magnet on the rod so that 'like' poles are facing each other (this upper magnet represents the prominence).


Opposite magnetic poles attract and similar poles repel. So the upper magnet appears to hover in space.


Sometimes this effect is used in executive 'toys' for office desks. Ever seen any? Watch out and see if you can spot them.

Image showing the experiment thats simulates the Sun's magnetic field

What you won’t be able to recreate in the classroom is the fact that the solar corona (air in the room) has a temperature of 1,000,000oC while the prominence (upper magnet) remains cool. No one is sure how the prominence is shielded from the corona’s heat - maybe you’ll be the solar adventurer who solves the mystery for us?




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