Lightning is a consequence of the existence of opposing electric charges between two centers of charge (within a single cloud, between a cloud and the ground, between one cloud and another, or between a cloud and the surrounding sky), causing a very strong attraction , breaking the ability of air insulation.
With this, there is a rapid movement of electrons from the air from one place to another. The electrons move so fast that they make the air around them light up (a flash known as lightning) and warm up, resulting in a sound shock wave (thunder).
The discharge is visible to the naked eye, hundreds of miles away, with sinuous trajectories and irregular ramifications, sometimes many kilometers long. When viewed from a distance, its luminosity spreads throughout the cloud and through the sky, although thunder can not be heard.
Some claim that it was the rays that, in causing fires, took the primates out of the trees and later showed the first humans the importance of fire. From ancient times the rays enchant and haunt mankind with its threatening and at the same time intriguing aspect, which was eventually incorporated into the myths and legends as an element of demonstration of the existence of powerful gods like the Greek Zeus, for example.
Benjamin Franklin proved the hypothesis of the electric origin of the rays by designing the lightning rods, in order to protect the buildings from the action of the rays. It was in the eighteenth century, practically, the beginning of the systematic study of electricity. At that time a theory was not known that explained the phenomenon of the storms and the rays that appeared in them.
The process of lightning formation has not yet been fully elucidated, there are controversies about its formation mechanism, but it is known that, in most cases, the discharge occurs after a concentration of charges, in which one can speak in centers of and is pursued in two distinct phases.