How does aurora occurs?why it is only seen in the polar region?

-The Earth has a magnetic field similar to a bar magnet, from the geographic South Pole to the geographic North Pole.

-Charged particles stream from the Sun and arrive in the Earth's vicinity.

-These charged particles undergo collisions in the Earth's vicinity which slows them down and they subsequently get trapped in spiral paths around the planet's magnetic field lines.

-The Earth's field lines become denser as they approach a pole.

-As the lines become denser the charged particles' path eventually turns back on itself.

-A particle spiralling along the field lines from the South Pole to the North Pole turns around at the North Pole spiralling back and heading southward.

-This effect is called magnetic mirrors.

-The aurora borealis and aurora austrealis is the consequence of the above effect.

-This occurs when the charged particles enter the atmosphere and excite the atoms in the air creating the visible colours.

-It is visible near the poles where the magnetic field lines dip toward the Earth's surface.