The Sun in ultraviolet light.
The high solar atmosphere (corona) shown here in ultraviolet light, is very rarefied. Collisions between particles are thus rare. The reason why the corona is so hot (1 or 2 millions Kelvin) is not known.
The gas emits UV because it is so hot. The picture was obtained by TRACE.
The loops trace magnetic field lines. They are found everywhere, but matter happens to concentrate more in some magnetic field lines which are like tubes that emprison the gas.
