What Comes First: Lightning or Thunder?

Popularly, we believe that lightning and thunder often come hand in hand during a thunderstorm, but have you ever wondered which phenomenon comes first?

Understanding the Mechanism

Although we perceive lightning and thunder together, with the flash of light generally occurring followed by the rolling thunder, the actual sequence of events is a bit different. The core event is the electrical discharge that creates lightning. This discharge rapidly heats the surrounding air, causing it to expand and form a shock wave—the thunder we hear.

The Speed of Light vs. Sound

Light and sound travel at vastly different speeds. Light travels at approximately 300,000 kilometers per second (186,000 miles per second), while sound travels much slower at about 340 meters per second. This significant difference in speed explains why we see the flash of lightning before we hear the thunder.

Evidence of Lightning and Thunder

When a lightning bolt occurs, it heats the air immediately around it, causing a rapid expansion. This expansion creates a shock wave, which we perceive as thunder. The lightning bolt itself is much more instantaneous, allowing us to see it first, followed by the thunder, which takes longer to travel through the air.

Near Simultaneous Occurrence: Lightning and Thunder

While the visible lightning and audible thunder may seem to occur together, in reality, the lightning happens first, and the thunder follows shortly after. In most cases, the thunder is the result of the lightning discharge, but there are rare instances of dry lightning. Dry lightning can occur without significant rainfall, often leading to wildfires.

Why We See Lightning Before We Hear Thunder

A person on the ground will see the lightning flash before hearing the thunder. This is due to the immense difference in the speed of light and sound. Since light travels much faster (around 300,000,000 meters per second), it reaches our eyes first, whereas sound travels at a much slower pace (around 340 meters per second).

In a thunderstorm, lightning and thunder do occur almost simultaneously. However, due to the faster speed of light, we perceive the lightning flash first, and the thunder follows shortly after as the shock wave propagates through the air.

Note: The specifics of when lightning and thunder occur can be influenced by various factors, including the proximity to the lightning strike and atmospheric conditions.