The Northern Lights are a luminous glow of the upper atmosphere which is caused by solar storms that travel from the sun, through space and enter Earth´s atmosphere. A solar storm is a stream of charged particles released from the upper atmosphere of the Sun. When the storm encounters Earth´s magnetic field, it travels down the field lines that connect at the poles. Atoms in the plasma interacts with atoms in the Earth´s upper atmosphere and produces the phenomenon called the Northern Lights or Aurora Borealis at the North Pole and Aurora Australis on the South Pole.
The speed of the solar storm determines the strength of the lights. It can be from around 250-800 km/s. The faster the storm is travelling through space, the harder it hits the Earth´s upper atmosphere. The charged particles in the storm collide with atmospheric atoms and molecules and transfer their energy. These gas molecules release that energy back out in the form of light. If the speed of the solar storm is around 250 km/s the lights can be hard to see with the naked eyes, but if particles collide with atmospheric atoms at the speed of 800 km/s, the lights will be strong – naked eyes auroras.
Earth´s atmosphere is mostly made up of oxygen and nitrogen. Atoms of nitrogen release blue light. Two nitrogen atoms bonded together release the color purple. The color of the Aurora also depends on altitude. Oxygen displays green light above 100km but turns reddish above 240km. When colors combine in the sky, they can produce other shades like yellow and pink.
The Northern Lights can last from a few minutes up to hours, depending on the magnitude of the incoming solar wind. Big solar flares accompanied by coronal mass ejections give us the bright lights.
If the aurora is faint, a full moon can affect visibility but if the aurora display is strong it does not matter. The moon can even add an extra effect to your photos and so can other lights as well, that we consider very little light pollution, lights that are not directed right at you.