What is lightning?

When raindrops and ice particles rub together in a thundercloud, they create and store a charge in the cloud. When the charge becomes too great for the cloud to hold, it suddenly discharges with a crackle and flash which we call thunder and lightning.

You've seen lightning bolts, streamers of charge moving from the bottom of the cloud to earth. But you may not have seen the streamers which move the charge from the center of the cloud to the bottom. They are usually hidden in the cloud. However, they have been photographed and studied. Scientist call them "J"-streamers. They form a "junction" for the small pockets of charge scattered throughout the cloud. Like streams and rivers, they feed charge into the main strokes to ground.

Some interesting lightning facts

• Ground strike length: 3-6 miles or more.
• Inter- and intra-cloud strike length: from a few yards to 90 miles or more. Typically 5-10 miles.
• Diameter: 0.6-5.0 in. Appears wider because of brightness.
• Temperature: Over 50,000 °F averaged over a few millionths of a second. Surface of the sun is only 11,000 °F.
• Air pressure in channel: 100 times atmosphere. This causes thunder.
• Occurrences: Average of 8 million ground strikes per day around the world year round.
• Current in a strike: Typically 10,000-20,000 amps; can be 200,000 amps or more. A light bulb uses about 1 amp.
• Flash duration: from 1/100 to 2 seconds. A flash consists of 1 to 23 rapid strokes.

Learn more

• All About Lightning by Martin A. Uman. Great for both neophyte non-technical and technical scientific readers.
• Lightning by Martin A. Uman. A very thorough examination of all aspects of lightning. Part of the Advanced Physics Monograph Series.