The Sun's 'wrong way around' heat

If you touch a glowing-hot lump of coal, you’ll surely burn your fingers. If, more cautiously, you bring your hand to within a few centimetres but no closer, you’ll feel the heat but you won’t get burned. The warm air surrounding the coal is not as hot as the coal itself.

Why, then, is the surface of the Sun (the photosphere) so much cooler than its atmosphere (the corona)? The photosphere's temperature is about 5500 degrees Celsius, while the corona is more than 2 million degrees. An unknown energy source appears to be pumping extra heat into the corona. Magnetic fields could be the culprit, but the precise mechanisms are still under debate.

Several teams among the UK Solar Physics community are studying detailed satellite images of the turbulent transition regions between the photosphere and the corona, trying to answer one of the most baffling mysteries of solar physics.