Lightning strikes once in a blue moon, right? Well, yes and no. Yes, lightning does strike about once every other day on average. No, you won’t see lightning on just any old moonless night. In general, lightning is a pretty uncommon phenomenon.
However, thunderstorms are common almost everywhere on Earth and if you’re reading this from outside the home of a brown bear or an Arctic fox, you’re probably somewhere where thunderstorms will be possible at some point during the summer season – that is to say somewhere humid and warm enough for moisture-rich air to rise above freezing temperatures and water to condense into rain clouds.
Even so, the lightning itself is still pretty uncommon; striking somewhere on earth only about once every 10 seconds. That leaves us with the question: How fast is lightning? Surely it can’t be as fast as the speed of light! Of course, it isn’t! But lightning can still attain speeds of around 180 million meters per second (130 million mph). That sounds pretty impressive until we remember that light travels at 299792458 m/s (300 million meters per second) – which means that light travels almost 10000000 times faster than lightning.
How Can We Measure the Speed of Lightning?
We know how fast light travels, so we can measure the speed of lightning by measuring how long it takes a flash of lightning to travel from the thundercloud to the ground. Since we can’t see the lightning in the thundercloud, we’ll need a way to see the lightning on the ground. Fortunately, there are scientists who specialize in doing just that.
Lightning “forecasters” make it their business to know when, where, and how often thunderstorms are likely to occur in a given area. They use lightning detection equipment – lightning sensors and cameras – to help us understand the nature of lightning and its relation to thunderstorms. By measuring the time it takes for a lightning bolt to reach the ground from the base of a thundercloud, we can determine the speed of lightning.
The Basics of Speed: How Fast is Lightning?
The nature of speed is a tricky thing to understand. A car that appears to be going 100 mph may in fact be moving only one foot per second. The speed of lightning is not a constant: It varies greatly depending upon the distance it has to travel and the conditions of the air (and ionosphere) through which it travels.
We can only give you the average speed of lightning, which is somewhere between 90 and 400 miles per second. It takes light about 1/10 of a second to travel 1 mile: So lightning travels 90 to 400 times farther than light does in the same amount of time. If you want to know how fast lightning is in meters per second, divide the speed in miles per second by 1/5,280. If you want to know how fast lightning is in kilometers per second, divide the speed in miles per second by 1/4,800.
Why is it so Fast?
Lightning is an electrical discharge caused by a build-up of charge in the atmosphere. The electricity that creates lightning comes from the ground, where electrons are transferred to the air by way of sand and dust particles. As the negatively charged particles rise, they are attracted to positively charged molecules in other parts of the atmosphere.
This creates a charge imbalance that can build until the air’s electrical pressure reaches a point where it can no longer be contained. The result is a lightning bolt that travels from the negatively charged cloud down to the positively charged ground. The fastest lightning is created by strong thunderstorms with large rising currents of air.
In these storms, a large amount of dust and sand on the ground creates a large amount of negatively charged particles, which are attracted to positively charged molecules in the rising currents of air. This creates a high amount of electrical pressure that results in fast-moving lightning bolts.
Lightning and the Speed of Sound
Technically, this is how fast sound travels, not how fast lightning travels. However, since we don’t know how fast lightning travels, it’s easier to talk about how fast sound travels. Sound travels through air at a speed of 342 m/s at sea level. The speed of sound is slower in cold, moist air, which is the kind of air that exists during thunderstorms.
In a thunderstorm, the temperature of the air can vary widely as it is heated and cooled. This variation in temperature causes the speed of sound to vary greatly, so different parts of a storm may have widely different sound speeds. In some places, the sound may travel at roughly 1/3 of its normal speed.
The Role of Electricity
The vast difference between the speeds of light and lightning comes down to the nature of electricity. A bolt of lightning is made up of electric current, which travels much more slowly than light, which is electromagnetic radiation.
The electromagnetic spectrum is a scale measuring the speed of different types of radiation. Photons – the particles of light – are the fastest objects in nature, traveling at 299792458 m/s. However, electrical current travels at a much slower speed – around 100,000,000 m/s.
Where Does the Energy Come From?
All that energy comes from the potential energy of water molecules in the air. The air molecules in the lower atmosphere are almost all very close to the ground and are warm. The warm molecules are much more likely to evaporate water than the cold molecules above. In other words, the warm air near the ground is much more likely to become water vapor than the cold air above. This means that there is a lot of water vapor right in the ground. Most of the water vapor is very close to the ground, within a few meters.
When lightning occurs, the water molecules are given a sudden, very large leap in energy, which sends them flying upward. Most of the molecules fly upward until they hit the warmer troposphere and then fall back to the ground. The fall back to the ground carries the water vapor with it, along with lots of extra energy. Some of the water molecules are still high enough when they fall back to the ground to freeze, forming ice crystals. The ice crystals help to cause the sound of thunder.
Lightning is very fast. It travels at a speed of around 180 million meters per second through the atmosphere, and even faster through the ground. That’s about 100,000,000 times faster than light travels.
The two travel at such different speeds because lightning is electrical current and light is electromagnetic radiation. Electrical current travels much more slowly than light, which is why lightning appears to be so much slower than light.