Why are auroras formed?

Maybe because the earth forgets to switch off the lights.

No.

Let me explain.

Our sun is a giant burning star.

It expels tons of solar wind into space.

Solar wind consists of super hot charged particles which are fatal.

So, should we use a big umbrella to protect ourselves from these particles?

No.

The earth's magnetic field acts like a shield and protects us.

Its field lines appear to emerge from the south pole and merge into the north pole.

Now, when the charged particles hit our magnetic field, most of them get deflected.

However, some of them flow along the earth's magnetic field lines to the poles and reach our upper atmosphere.

Here, these particles collide with oxygen and nitrogen.

This causes them to give off various colors of light which are called auroras.