Great video from NASA on the northern lights and what they are about
Before we dive into understanding “what are the northern lights” it is important to understand couple of facts about the space surrounding our Earth. These are mainly things we can´t see with our eyes. One of these things are the air we breath. It is in fact a mixture of several gases – mainly nitrogen and oxygen, but with some traces of hydrogen, helium and some other minor compounds.
What are the northern lights?: The earth as a field of magnet
The air is something we cant see but another thing is actually the magnetic field that surrounds the Earth. In similar manner as if you have played with a bar magnet and iron filing you have seen how it forms the curved patterns in the magnetic field. The magnet is actually deep in the core of the Earth. As we cant see the magnetic field we normally represent it by drawing lines. Lines that go into and out of the Earth where the poles are. When the lines area closer the field is stronger.
One more thing is invisible and that is the charged particles called plasma. It is in fact a space around the Earth. These particles move in a special way – and are in fact guided by the field as if they were wires. They are the “ammunition” of an aurora.
Powered by the sun
The very quick answer to how the northern lights happen is that electrically charges particles move along the field lines, all the way up to the upper atmosphere, where they collide with gas atoms – and this causes them to give off some light. This all is powered by what is called solar wind, coming from the sun.