A spectacular night-time display of coloured light seen best against a dark sky inside the auroral zone, which is 3° to 6° wide and between 10° and 20° of the magnetic pole; a similar phenomenon in the southern hemisphere is known as the Southern Lights (Aurora Australis). It appears as a glow or as curtains that move and change constantly. The lights appear when charged particles in a strong solar wind, caught in the Earth’s magnetic field, enter the atmosphere and collide with and import energy to atmospheric particles, which then return to a lower energy state, releasing photons as they do so at wavelengths, hence colours, corresponding to the particles emitting them.