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We intuitively understand the direction that energy travels -- from the thing with energy to the thing with less energy. That's why the second law of thermodynamics is among the first things you learn in science class that makes you say, "Well, I could have told you that." If you're too hot, you move away from the campfire, not toward it. You don't need science to tell you that heat energy travels from the hot thing to the less-hot thing. Well, everywhere in the universe except the sun.

There's a discrepancy between what science says should happen and what the sun actually does, and it's known as the sun's coronal heating problem. Essentially, when heat leaves the sun, the laws of thermodynamics just totally break down for a few hundred miles, and nobody can quite figure out why. The facts are pretty straightforward; the sun's surface sits comfortably at a blazing temperature of roughly 5,500 degrees Celsius. No problem there. However, as the heat travels from the sun's surface to the layer a few hundred miles away from its surface (known as the sun's corona), it rises to a temperature of 1,000,000 degrees Celsius. Which is 995,000 degrees Celsius, or 1,791,000 degrees Fahrenheit, or 1 billion gigawatts per 1/4 gigabyte jiggawatt hour (metric) hotter than it has any right to be.

He's a loose cannon! The heat source (the giant ball of nuclear explosions and plasma) should be the hottest thing, not the empty vacuum of space around it. This is the only instance in the known universe where the thing doing the heating is actually cooler than the thing it's heating. And it's been plaguing solar physicists worldwide since they discovered the little disagreement reality has with our universe in 1939. How is it possible that the area around the sun is about 200 times hotter than its surface?

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Don't look too closely at your microwave oven, it might blow your mind... – user2963 Jan 25 '12 at 0:00
I must admit that was funny – Jack Jan 25 '12 at 1:44
Glad you could appreciate it.. I do think this is a pretty interesting question, but you've got some inaccuracies in wording that should be fixed. – user2963 Jan 25 '12 at 4:09
Jack, please cite properly if you intend to use other people's articles. Question is a copy of #6 here:… – Carsten Jan 25 '12 at 12:38
I thought he was pretty sophisticated until I realised that he copied the entire question from somewhere else. – James Kujareevanich Jul 22 '12 at 15:04

6 Answers 6

The "heating things hotter than itself" only applies to thermal radiation.

I'm not an expert, but the corona could be heated by absorption of high energy particles from within the sun, from it's magnetic field, or from a variety of non-thermal sources.

edit: Wikipedia has a description of the current theories

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have a look at

This seems to me a pretty thorough description of the physics involved, and I think we can regard Scientific American as a reasonably reputable source!

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I know this can be silly but is it not the same in case of a simple candle, where we can pass our finger through the bottom or center portion of the candle but not the upper part of the flame which is hotter.

Can it not be the case with the sun.

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but then how come farts (pretty cold with respect to the flame) heat flames? – propaganda Jan 25 '12 at 11:27
because its a fuel. hope that answers your question so that you don't have to take the trouble of posting it. – shrawan zadoo Jan 25 '12 at 11:38

CORONAL heating problem

    chromosphere            !!!              !!!  
                            !!! sunspot(cold)!!!


        photosphere          !!! hot region !!!  

legend and explanation:

--- - sun 'surface' i.e. top of photosphere that is transparent to radiation

| - radiation flow thru the sun surface

__ - sunspot . It is a cold feature, i.e. it blocks the upcaming radiation and inevitably HEAT the region under the sunspot.

!!! - escaped particles strongly heated in the hot region bellow sunspots that must escape thru the outer limits of the sunspot. The escaped matter is ionized and its motion creates the magnetic field and not 'the magnetic field creates ...'.

In consequence there is no contradiction with Thermodynamic Laws.

Note: this is part of an original idea on sunspots origin from my friend Alfredo Gouveia Oliveira partially undisclosed at outramargem-alf (label SOL) (Creative Commons Attribution-No Derivative Works 3.0 Unported Licence)

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Perhaps the outer layers of sun are transparent to thermal x-rays generated in the very hot core of the sun.

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I don't think this holds together...the bulk of the star is a plasma, so it should be pretty opaque in all bands (due to Compton scattering off of the free electrons). – dmckee Jan 25 '12 at 0:15

Could be that the ejected plasma combined with intense magnetic field creates higher plasma velocities, pehaps momentarily greater than lightspeed, creating "lightless" sunspots while violently altering the electro-magnetic frequencies/pulses, resulting in a superheated corona. -AMFM-

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