Lightning is a natural phenomena that occurs when a discharge of static electricity moves from a cloud to another cloud or part thereof, or from a cloud to ground. (Or rarely, from ground to a cloud) Typically associated with cumulonimbus clouds, lightning has the characteristic of producing bright flashes, followed by thunder as the heated air around the flash exceeds the speed of sound.

Water droplets rub against each other during a storm. Every drop becomes charged with a tiny bit of electricity, either positive or negative. Updrafts of wind carry the positively charged particles (small ice particles) to the top of the cloud and negatively charged particles (large water droplets) to the bottom of the cloud. Since there are billions of droplets in a cloud, a cloud carries a huge charge of electricity. When the negative part of a cloud moves near the positive part of another cloud or vice versa, electricity in the form of lightning, jumps from the negative part of a cloud to the postive part of another. Since the earth is positively charged during storms, lightning sometimes jumps from a cloud to the earth.

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Some various facts about lightning:

• Lightning can be often seen as white or white-yellow, although it can appear to have other colors depending on the background.
• The temperature of the air around a bolt of lightning is about 54,000ºF (30,000ºC), which is about six times hotter than the surface of the sun.
• Roy Sullivan was a park ranger who was hit by lightning seven times between 1942 and 1977.
• A person does not usually die from a lightning strike as long as the electrical energy does not go through their heart or spinal column. People who are given CPR immediately after being struck usually survive.
• Lightning can strike the same place more than once. The Empire State Building can be struck several times during the same storm (12 times in one recorded storm).
• The visible portion of a bolt of lightning can vary in length, usually ranging from 300 yards in mountainous areas, to 4 miles in flatlands. The average length is about 1 mile, but some as long as 20 miles have been recorded.
• The width of a lightning bolt is very narrow, around 1/2 inch. It is surrounded by a corona envelope, which is a glowing discharge which can be 10-20 feet in diameter.
• The speed of lightning can vary from 100 to 1,000 miles per second for the initial track and as much as 87,000 miles per second for the return (nearly half the speed of light).
• A stroke of lightning discharges from 10 to 100 million volts of electricity. The average strike has about 30,000 amperes.
• To roughly calculate the distance of a strike, count the number of seconds from the time it is seen until the time it is heard and then divide by five to get the distance in miles.
• When lightning strikes an area of dry sand, it forms a root-shaped solid chunk of silicon called a fulgurite.

Most of this information was paraphrased from The Handy Science Answer Book.

Lightning or bullet: quick chess. Officially, shorter than "3 0" time controls, i.e. 0 1, 0 2, 0 3, 0 4, 1 0, 1 1, 1 2, 2 1 (time controls are in minutes start - seconds increment). Played often on Internet Chess Servers such as FICS or ICC rather than OTB, for practical purposes.

View information online at: http://www.checkmate.de/.

The lightning tonight looks like a fissure in the air. It's the first time I've ever seen an actual lightning bolt, instead of just a flash of light across the sky. When it strikes the earth, it feels like something is trying to reach out from inside the chasm and pull part of this world back with it, but the crack closes too quickly for it to catch anything.

I start counting:

"One-Mississippi

Two-Mississippi..."

before I realize I am in the storm. I am a part of it.

The lightning gets closer. There is a bang on the door that somehow drowns out the thunder. I can feel the impact on the other side. A horrid scratching sound penetrates deep into my skull. I pray the lock will hold until the storm subsides.

Another clap from the heavens and the room goes black.

The amount of electricity in a bolt of lightning is huge, and plenty sufficient to kill you should it come into contact with your body. Whilst the chances of you being struck by lightning are mercifully slim, it does happen.

• Logic suggests that the safest place to be during a lightning storm is inside. This is pretty much true, being within a building is safe, as long as it is stable.
• Odd as it may seem, a car is considered a very safe place to be during a storm (see note at end).
• If you are unable to take shelter, do not shelter under a tree or any other tall object. Whilst the lightning is more likely to strike the tree rather than you, the electricity can jump to you from the tree, and this is not to mention the risk of the tree falling and crushing you.
• The advice I was always given was to crouch with your head as low as possible. It is also advised to keep contact with the ground to a minimum (ie crouch on the balls of your feet).
• Using telecommunications equipment during storms is generally a bad idea, as the you can recieve a nasty electric shock transmitted down the line from a pylon struck by lightning. This kills several people a year. Mobile phones and cordless phones are somewhat safer, with the latter ensure you are away from the base unit. Unplugging telecoms equipment full-stop is a good idea anyway, I've lost at least 3 modems through lightning storms, and they weren't covered by the warranty.
• I've also been told that the use of any electronic equipment, including computers, is also dangerous due to the risk of shock being transferred from the mains to you, through a keyboard or headphones for example. Whether this is erring a little far on the side of caution I couldn't say. Better safe than sorry, perhaps.
• Any unnecessary contact with water is, needless to say, a bad idea. This extends to basins, taps, baths and showers.

Basically, get inside. Failing that, get in a car. And if you ARE outside with no shelter to run to, avoid trees, keep low, keep your head lower, and minimise contact with the ground.

Teiresias writes: Reason that cars are safe is due to a common misconception about lightening, there is a faint 'leader stroke' from the ground to the cloud which allows the cloud to earth on the downstroke. The reason cars are safe is that 4 blocks of rubber insulate the car from the ground thus preventing the leader stroke from going up.The leader stroke is also why lightening hits the highest point in the vicinity.

Introduction

Lightning is a common manifestation of the raw power of nature: something as humble as water and air can shatter rocks, set fire to buildings and kill people. We all know what it looks like: A big line of angry bluish white light, combined with a thunder that comes a few seconds later. But, how does it work? Why does it happen? It turns out the answer to that question is not entirely clear.

The physics of lightning

Lightning starts with a large cloud. In this cloud, the rubbing of ice crystals against each other liberates electrons. For some reason that's not currently understood, the negative crystals go to the bottom and the positive ones go to the top, although the opposite-positive bottom, negative top- also happens. This produces an electric field, between the top and bottom of the cloud and the bottom of the cloud and the earth.

The next step is the formation of streamers. The electric field causes free electrons to accelerate, and these ionize air molecules. So, now we have free positive and negative charge, creating a plasma. The electric field causes these charges to reorganize. The head of this thing, called a streamer, becomes negative, and the part behind the head becomes positive. This field compression causes enhanced ionization. This means the streamer, known as a stepper leader, can propagate. Due to inherent instabilities in this process, the streamer will have a tendency to branch. In less than a second, typically, a whole tree-like structure of streamers becomes attached to the cloud. In this short time, the plasma behind the streamer heads hasn't recombined fully, so the whole tree is a moderately good conductor of electricity, as it contains free charges.

When the tree, with the negatively-charged tips, comes close to the ground, the electric field caused by the tips causes the ground, and in particular high, pointy things on the ground, to send out their own streamers. At some point, a streamer from the ground and from the cloud will connect. At this point, we have a conductive channel, over which there is an enormous voltage difference, in the order of millions of volts.

Now, things go very, very fast. There is nothing stopping an electric current from flowing through the channel between earth and cloud. As the current increases, the plasma will become hotter, increasing ionization and, consequently, conduction. The size of the plasma will also increase, reaching typical sizes of a centimeter or so. These mechanisms cause even more current to flow. In principle, this process is self-increasing, until the charge separation has been rectified. This plasma is what we commonly call lightning. The plasma reaches a temperature in the order of 25,000 K. There will be many free electrons and ions. Hot electrons can excite atoms and molecules, causing them to emit light. This is the visible lightning.

The air has been suddenly heated up from 300 to 25,000 K, and extra particles have been produced, in the form of free nitrogen atoms, free oxygen atoms, all sort of atomic and molecular ions and electrons. Via the ideal gas law we see that the pressure is proportional to both temperature and the amount of particles. So, suddenly the local pressure has increased hundredfold. The subsequent explosion of this high-pressure region into the cool surrounding gas produces awesome shockwaves and is audible as thunder. Because sound travels much slower than light, you will hear the thunder generally after you have seen the lightning. As a rough guide, the lightning is one kilometer away for each 3 seconds of time difference.

The residual plasma recombines after the lightning strike. However, the free nitrogen and oxygen atoms do not necessarily recombine to nitrogen and oxygen molecules. Some will recombine to nitrous oxides, NO_x, and others to ozone, O₃. These substances are the cause of the acrid smell after a thunderstorm.

How to prevent being struck by lightning

Being hit with a hot plasma bolt that conducts several kiloampères of current can be extremely detrimental to one's health. Generally, extensive burns, both where the bolt enters the body and where it leaves the body occur. The biggest danger however is that the massive current may cause a cardiac arrest which is fatal if not treated. In short, we don't want to be hit by lightning. So, how can we avoid it?

• First, establish how far the lighting is away from you. If it's 5 kilometers away, there is little need to get all excited yet, as it may not come near.
• If you are in a city, don't sweat it. There is likely a high building nearby, which has a much greater chance of getting the lightning strike than you have. However, unplugging nonessential electronic equipment can be a good idea, as the current may pass through the electric wiring in the ground, and completely toast every electric device that is plugged in. And most insurances are bitches when it comes to paying for them. Fuses offer little protection, as their melting time is too long. Do stay away from large windows and metal piping.
• If you are in a car, just stay in. The metal of your car is an excellent conductor, and the current will flow trough the outer metallic shell rather than through you. If your car is hit by lightning, it may be a good idea to gently bump an obstacle to let the residual charges drain.
• In a forest, just take shelter under a tree, preferably one that isn't very tall. The chance that your tree will be hit is pretty minimal.
• If caught in the open, you may have a problem. Don't take shelter under high objects, as these attract lightning. Don't be the highest object yourself. If you are the highest object, squat, while touching the ground only with your feet. If you lie down, you have a very large contact area with the ground, and nearby lightning strikes may harm you, by draining their charge not only through the ground but also through you. Professor Pi points out that putting your feet close together is a good idea, and he's right, as it will minimize the potential difference between them, thus making it less likely for current to flow through your body.

Conclusion

Lightning is a beautiful manifestation of the power of nature. Reaching temperatures several times more than the temperature of the surface of the sun, producing shock waves that can be heard from several kilometers distance, and reorganizing the very molecules of the air, it continues to be a symbol of speed and power. It is, like most things powerful, dangerous, and proper precautions should be taken not to be struck by it.

Sources:

• http://science.howstuffworks.com/lightning.htm
• http://nis-www.lanl.gov/~stanleym/dissertation/node17.html
• http://homepages.cwi.nl/~carolyn/NWO/poster2003.pdf
• http://hypertextbook.com/facts/1998/MathieuLo.shtml
• Lecture notes from a lecture by Professor Raizer
• My own understanding of plasma physics

Light"ning (?), n. [For lightening, fr. lighten to flash.]

1.

A discharge of atmospheric electricity, accompanied by a vivid flash of light, commonly from one cloud to another, sometimes from a cloud to the earth. The sound produced by the electricity in passing rapidly through the atmosphere constitutes thunder.

2.

The act of making bright, or the state of being made bright; enlightenment; brightening, as of the mental powers.

[R.]

Ball lightning, a rare form of lightning sometimes seen as a globe of fire moving from the clouds to the earth. -- Chain lightning, lightning in angular, zigzag, or forked flashes. -- Heat lightning, more or less vivid and extensive flashes of electric light, without thunder, seen near the horizon, esp. at the close of a hot day. -- Lightning arrester Telegraphy, a device, at the place where a wire enters a building, for preventing injury by lightning to an operator or instrument. It consists of a short circuit to the ground interrupted by a thin nonconductor over which lightning jumps. Called also lightning discharger. -- Lightning bug Zool., a luminous beetle. See Firefly. -- Lightning conductor, a lightning rod. -- Lightning glance, a quick, penetrating glance of a brilliant eye. -- Lightning rod, a metallic rod set up on a building, or on the mast of a vessel, and connected with the earth or water below, for the purpose of protecting the building or vessel from lightning. -- Sheet lightning, a diffused glow of electric light flashing out from the clouds, and illumining their outlines. The appearance is sometimes due to the reflection of light from distant flashes of lightning by the nearer clouds.

 

© Webster 1913.

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Light"ning (?), vb. n.

Lightening.

[R.]

 

© Webster 1913.