why does a flare happen at all?

The biggest question is where on Earth, or rather where on the Sun, does the energy that powers solar flares come from? This isn't an easy question to answer, but we're working on it.

Although we suspect that the Sun's magnetic field is a big part of the answer, there's a problem because we can't actually see the Sun's magnetic field directly. We have to rely on monitoring the way it controls the Sun's plasma. Images of the plasma show us that the magnetic field can be as messy as a bowl of spaghetti.

Here is a movie of a flare seen in ultraviolet radiation with the TRACE satellite. Notice how complex it is. The bright cross shape happens when the flare is at its brightest. This movie covers a time period of about 5 hours.

The bright loops in this picture from TRACE certainly give some idea of how complicated solar magnetic fields can be. You can imagine how difficult it is to work out how the energy is released to make solar flares happen.

What exactly is this mess of a magnetic field to do with solar flares? Well, when a magnetic field gets this tangled up there comes a point when it just can't take it anymore and - SNAP... the field "unwinds" and out comes a colossal amount of energy. Ever felt like that yourself?