How come the sun's photosphere(6000k) is colder than the corona(2m K), even thought corona is further away?

Answer 1

Because fusion doesn't happen inside the Sun's core. The corona is about 300 times hotter than the photosphere. Sunspots shows us an interior of the Sun that is even cooler than the photosphere.

This is because huge electric currents are passing over the Sun. The charge per cubic meter is too small a difference for our instruments to detect, but it's so massive that it really adds up fast. We pick up the movements of these currents though, and call it the solar wind.

Problems with the current model of the sun as continuous fusion reaction, releasing energy from the core:

Missing neutrinos
Temperature of the halo-like corona is 300 times that of surface
Rotates faster at equator, faster on surface
Solar wind accelerates upon leaving the Sun
Sunspots reveal cooler interior
Sunspots travel faster than surrounding surface
Sunspot penumbra (interior walls) reveal structured filaments

http://i43.photobucket.com/albums/e397/Bigpappadiaz/sun.jpg

http://i43.photobucket.com/albums/e397/Bigpappadiaz/sun2.jpg

The most detailed pictures ever taken of the Sun reveal the insides of striking snake-like filaments that reach from bright portions of the solar surface into the dark hearts of sunspots. Researchers at the Royal Swedish Academy of Sciences in Stockholm discussed the images in the journal Nature. One researcher commented: "A dark-cored filament looks like a glowing snake with a dark stripe painted along its back. The 'head' of the snake is often a complicated feature where the stripe splits up among many bright points."

The scientists also identified canal-like structures in the so-called penumbra of sunspots that "could also be described as a pattern of cracks," the researcher said. The penumbra straddles a sunspots dark core and brighter regions elsewhere on the solar surface. "Whatever metaphors we use for these features, one should remember that everything is just glowing gas."

There is a temptation to simply equate the penumbral filaments with gargantuan lightning bolts, but the features do not match all that well.

A typical lightning flash lasts for 0.2 seconds and covers a distance of about 10 km. The penumbral filaments last for at least one hour and are of the order of 1000 km long. If we could scale a lightning bolt 100 times we might have a flash that lasted between 20 and 200 seconds and was 1000 km long. The lifetime is too short.

http://i43.photobucket.com/albums/e397/Bigpappadiaz/firetube.jpg

This shows an artificial tornado of fire, the bright edges to the vortex near the base, so there is another familiar form of atmospheric electric discharge that does scale appropriately and could explain the mysterious dark cores of penumbral filaments. It is the tornado! Tornadoes, like the one pictured here, last for minutes and can have a diameter of the order of one kilometre. Scale those figures up 100 times and we match penumbral filaments very well. And if the circulating cylinder of plasma is radiating heat and light, as we see on the Sun, then the solar 'tornado' will appear, side on, to have a dark core.

http://i43.photobucket.com/albums/e397/Bigpappadiaz/050616sunspotropes.jpg

We can see here a twin bridge crossing a sunspot. This is indicative of electrical activity. I hope this helps you better understand the Sun.

Answer 2

What heats the corona is one of the unresolved questions in astronomy. Recent discoveries using the SOHO and TRACE space-based solar observatories suggest that it is due to fluctuating magnetic fields on the surface of the Sun.

It seems a bit upside-down to have the corona hotter than the surface (photosphere), but there is no paradox in the energy balance. The corona is so tenuous that its energy content is relatively small despite its very high temperatures.

Answer 3

The plasma in the corona is whipped around by flux lines in the Sun's magnetic field breaking and flicking them around. Don't take this analogy too far, but it's a bit like the tip of a whip exceeding the speed of sound when you crack it.

Answer 4

Because heat travels in the opposite direction of gravity, heat rises. That's how hot air balloons work, heat travels in the opposite direction of gravity, which makes the hot air balloon lift. So heat rises to the upper part of the sun's atmosphere. Way, way up in earth's atmosphere, there's a place of very hot air. It's about 1,000ºC...is what I heard. Space ships have to be careful when they are going through there.

Answer 5

The same reason that the top of a flame is hotter than the base of a flame.

Answer 6

the corona has more activity