Lightning and Thunder

Lightning is a sudden, powerful electrical discharge that occurs during thunderstorms. Inside a storm cloud, strong updrafts and collisions between ice particles and water droplets separate electric charge, leaving the upper part of the cloud positively charged and the lower part largely negative. When the difference in charge becomes large enough to overcome the insulating effect of the air, a rapid discharge takes place, either within the cloud, between clouds, or between the cloud and the ground.

The discharge heats the surrounding air almost instantly to an extremely high temperature, causing it to expand explosively. This rapid expansion produces a shock wave that is heard as thunder. Because light travels far faster than sound, the flash is seen before the thunder is heard, and the delay between them indicates how far away the strike occurred. The brightness and branching shape of a lightning bolt reflect the path the discharge follows through the air.

A rare and poorly understood phenomenon called ball lightning is sometimes reported as a glowing sphere that appears during storms, though it remains difficult to study. Because lightning seeks the easiest path to the ground, tall structures are especially exposed, and lightning protection systems use conductors and grounding rods to safely carry the current into the earth. Factors such as humidity, air density, and temperature influence how storms develop and how readily discharges occur.

Frequently asked questions

What causes lightning?

Charge separation inside storm clouds builds up an electric field that eventually discharges as lightning when it overcomes the resistance of the air.

Why do we see lightning before hearing thunder?

Light travels much faster than sound, so the flash reaches the eye almost instantly while the thunder arrives moments later.

How does lightning protection work?

Conductors and grounding rods give the discharge a safe, low-resistance path to the earth, steering it away from the structure being protected.