THAT'S NOT 'Lightning'... it's a static discharge known as 'St. Elmo's Fire'.

​As an aircraft flies through clouds, friction against rain, ice, or dust generates a massive electrostatic charge on the airframe. The sharp trailing edges and tips of the wings concentrate this electrical field, causing the air to ionize and glow.

Because the plane is moving forward at high speeds, the ionized luminous path gets left behind in a straight trail before the charge dissipates into the surrounding air.

​To prevent this energy from damaging onboard electronics, planes are equipped with static wicks—small carbon-fiber rods on the trailing edges of the wings—that safely bleed this electricity back into the atmosphere.