A giant electrical spark

What Is Lightning?

Lightning looks like the sky splitting open. It is really a giant electrical discharge, created when storm clouds build enough charge to tear through air.

The short answer

Lightning is a sudden, large-scale electrical discharge. Charge builds up inside a storm cloud until the electric field becomes strong enough to rip through the air. The result is a plasma channel that carries billions of watts in a fraction of a second.

Lightning bolt striking during a nighttime storm with dark clouds overhead

Temperature

Around 30,000 K

Duration

Under 1 second

Charge source

Storm cloud

Thunder cause

Rapid air expansion

Visual answer

How a lightning bolt forms and travels

A lightning strike involves several steps happening faster than the eye can follow.

Charge separation

Ice crystals and water droplets collide inside the cloud, separating positive and negative charges.

Stepped leader

An invisible channel of ionized air extends down from the cloud in steps toward the ground.

Return stroke

When the leader connects with a rising channel from the ground, a massive current flows. This is the bright flash.

Thunder

The stroke instantly superheats the surrounding air to extreme temperatures. It expands explosively, creating the sound wave.

How charge builds

Why charge builds up in storm clouds

Inside a thunderstorm, ice crystals and water droplets are constantly colliding as they are pushed around by powerful updrafts and downdrafts.

These collisions transfer electric charge. Lighter particles carrying positive charge get carried to the top of the cloud. Heavier negatively charged particles accumulate in the lower part.

The electric field between the bottom of the cloud and the ground below grows stronger until it overcomes the insulating resistance of the air.

Tiny note

Lightning is the fourth state of matter

When the electric field tears through air, it rips electrons from gas molecules and creates a plasma channel. This channel is about as wide as a thumb but reaches temperatures around five times hotter than the surface of the sun, briefly outshining it in ultraviolet light.

Direction myth

Does lightning travel from cloud to ground?

What people think

Lightning shoots down from the cloud to the ground.

That is how it looks to the naked eye.

What actually happens

The bright flash travels upward.

The stepped leader moves downward invisibly. Once it connects with a rising channel from the ground, the powerful return stroke travels upward. The bright flash most people see is the return stroke, moving from ground to cloud.

Types of lightning

Different kinds of lightning

Cloud-to-ground

The most familiar type. About 25 percent of all lightning.

Intracloud

Occurs entirely within a single cloud. The most common type overall.

Cloud-to-cloud

Passes between separate clouds.

Sprites and elves

Rare electrical phenomena above storm systems, reaching into the upper atmosphere.

Why thunder follows

Why thunder always comes after the flash

Light travels about a million times faster than sound. The flash reaches your eyes almost instantly.

The sound of thunder, caused by the rapid expansion of superheated air around the lightning channel, travels at roughly 343 meters per second.

Every 3 seconds between the flash and the thunder equals about 1 kilometer of distance to the strike.

Tiny note

The simple answer

Lightning is a giant electrical spark caused by charge buildup in storm clouds. When the electric field grows strong enough to break through the air, a plasma channel forms and carries an enormous current. Thunder is the sound of the surrounding air exploding outward from the heat.

Quick answers

Common questions

What causes lightning?

Charge separation inside storm clouds builds up until the electric field is strong enough to ionize the air and create a conductive channel.

How hot is lightning?

The plasma in a lightning bolt reaches around 30,000 Kelvin, roughly five times the surface temperature of the sun.

Can lightning strike the same place twice?

Yes. Tall structures like the Empire State Building are struck dozens of times per year. Lightning preferentially follows existing ionized channels and conductive paths.

Why does thunder rumble instead of being one sharp crack?

A lightning channel can be several kilometers long. Thunder from different parts of the channel reaches you at different times, spreading the sound out into a rolling rumble.

Is it safe to be inside during a lightning storm?

Inside a solid building or a hard-topped vehicle is generally safe. Avoid contact with water, electrical outlets, and corded phones during a storm.

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