They are pretty common, specially when there are solar flares.
Phisics call the magnetically charged particles coming from the sun "sun wind" when it comes to earth it is displaced following the lines of the magnetic field of earth, when those charged particles hit the medium/lower atmosphere molecules they emit photons (light). The color of the "aurora boreal" depends on what type of atoms the particles are colliding(and i guess that as the atmosphere has layers of different density gasses it can give an idea of the altitude where the collisions are taking place).
That also means that all the radiation wich should collide with the earth is deflected to and concentrated on (or "near" to) the magnetic poles... and it comes very close to the ground...

Also i would like to spend a week anywhere on the "artic polar circle" I´ve heared that there, due to sun/earth relative positions, theres a week a year when the sun never sets, just travels arround the sky...