What causes the beautiful Auroras on the north and south magnetic poles?
Straight from wikipedia:


  Auroras are associated with the solar wind, a flow of ions
  continuously flowing outward from the Sun. The Earth's magnetic field
  traps these particles, many of which travel toward the poles where
  they are accelerated toward Earth. Collisions between these ions and
  atmospheric atoms and molecules cause energy releases in the form of
  auroras appearing in large circles around the poles. Auroras are more
  frequent and brighter during the intense phase of the solar cycle when
  coronal mass ejections increase the intensity of the solar wind.
  
  Auroras result from emissions of photons in the Earth's upper
  atmosphere, above 80 km (50 mi), from ionized nitrogen molecules
  regaining an electron, and oxygen atoms and nitrogen molecules
  returning from an excited state to ground state. They are ionized
  or excited by the collision of solar wind and magnetospheric particles
  being funneled down and accelerated along the Earth's magnetic field
  lines; excitation energy is lost by the emission of a photon, or by
  collision with another atom or molecule:
  
  
  oxygen emissions: green or brownish-red, depending on the amount of energy absorbed.
  nitrogen emissions: blue or red; blue if the atom regains an electron after it has been ionized, red if returning to ground state from an excited state.
  
  
  Oxygen is unusual in terms of its return to ground state: it can take
  three quarters of a second to emit green light and up to two minutes
  to emit red. Collisions with other atoms or molecules absorb the
  excitation energy and prevent emission. Because the very top of the
  atmosphere has a higher percentage of oxygen and is sparsely
  distributed such collisions are rare enough to allow time for oxygen
  to emit red. Collisions become more frequent progressing down into the
  atmosphere, so that red emissions do not have time to happen, and
  eventually even green light emissions are prevented.
  
  This is why there is a color differential with altitude; at high
  altitude oxygen red dominates, then oxygen green and nitrogen
  blue/red, then finally nitrogen blue/red when collisions prevent
  oxygen from emitting anything. Green is the most common of all
  auroras. Behind it is pink, a mixture of light green and red, followed
  by pure red, yellow (a mixture of red and green), and finally, pure
  blue.