Elsewhere Lab

Field note 001 · AtmosphereInteractive

Which way does
lightning really travel?

A bolt appears all at once to the eye. Slow the event down, make your prediction, and trace what happens before the brightest moment.

Build the channel

Scroll to investigate

Experiment 001 · Follow the flash

First predict.
Then look closer.

Make a prediction, watch the whole event, then investigate it one stage at a time. The answer stays hidden until the sequence reaches its brightest moment.

01 · Predict

Which way does the brightest part travel?

Choose before you press play. There is no penalty for changing your mind.

Two Elsewhere Lab scientist characters examining the question

Choose an answer, then watch the sequence.

02 · Observe

Watch the whole event.

Try to follow the faint violet path first. The bright amber pulse comes later.

Interactive formation of a cloud-to-ground lightning flash A storm cloud, downward stepped leader, upward streamers, attachment, and upward return stroke. CHARGE SEPARATESGROUND / POSITIVE CHARGESTEPPED LEADER ↓STREAMERS ↑CHANNEL CONNECTSRETURN STROKE ↑
Stage1of 5
Now showingThe storm becomes a battery.
03InvestigateStep through the evidence

01 — BEFORE THE FLASH

The storm becomes a battery.

Collisions between rising ice crystals and graupel help separate charge inside the cloud. The lower region becomes predominantly negative.

Source: National Weather Service ↗

Playback timing is slowed and illustrative. It does not reproduce real elapsed time.

Your predictionChoose an answer above, then play the sequence.

04 · Compare

Two directions.
One channel.

The developing path and the brilliant return stroke are related events, but they do not move the same way.

Downward leader and upward return stroke compared A violet stepped leader moves from cloud to ground. After connection, an amber return stroke propagates from ground to cloud along the same channel. 1 · PATH DEVELOPS DOWN 2 · BRIGHT PULSE GOES UP One channel · shown in sequence

05 · Take away

The faint stepped leader develops downward; after attachment, the brightest return stroke propagates upward.

Revisit your prediction ↑

Evidence at a glance

Lightning develops in both directions. The pathfinder comes down. The brightest pulse goes up.

Typical estimate≈ 50 m

Length of one stepped-leader advance. NWS ↗

Approximate speed~200 million mph

Upward propagation of the visible return stroke. NWS ↗

Scientific care

What this experience shows—and simplifies.

Established

What the evidence supports

For a common negative cloud-to-ground flash, a branched stepped leader develops downward, upward streamers participate in attachment, and the bright return stroke then propagates upward through the completed channel.

Illustrative

What the diagram simplifies

The channel geometry, colours, brightness, distances and playback timing are designed for comparison. They are not a scale model, and the animation shows one stroke rather than every possible flicker or subsequent stroke.

Scope

What it does not claim

Lightning also occurs within clouds, between clouds, as positive cloud-to-ground flashes and as upward-initiated events. Those forms can follow different sequences.

Published 11 September 2026 · Content reviewed 11 September 2026

Report a correction by email ↗
Primary sources used in this storyNWS · Thunderstorm electrification ↗NWS · Negative cloud-to-ground flash ↗NWS · Attachment to ground ↗NWS · Return stroke ↗NWS · High-speed observations ↗

Explore next · Sound & vibration

How does sound make shapes?

You’ve traced a lightning flash. Now change a tone and watch sand organise into a pattern on a vibrating plate.

Try the sound experiment

Continue exploring

Get the next explanation.

New visual stories about the hidden science of everyday life, the universe, and reality.

Follow on YouTube