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Lightning

© Patrice Bentham

I don't mind a thunderstorm if it's not extremely violent or loud. Lightning flashing every second and loud rolling peals of thunder can be frightening. I just had a thought! May be if I learn something about lightning, a storm won't bother me so much. But don't count on it:-).

The Franklin Institute's Online Lightning site, http://sln.fi.edu/weather/lightning/ligh... , is a straightforward readable introduction into the phenomenon of lightning. A brief section on the history of lightning recounts Benjamin Franklin's famous experiment. Lightning Science tells us what exactly lightning is-opposites attracting. Did you know that there are three different types of lightning bolts-cloud to ground (forked), intracloud (within clouds) and intercloud (between clouds)? Intracloud and intercloud both occur in the sky and never touch ground. The National Geographic's site Lightning-The Shocking Story, http://www.nationalgeographic.com/lightn... refers to the different types of lightning bolts as cloud (intracloud) and spider (intercloud). It also has a picture of a strange form of lightning - ball lightning. Ball lightning usually occurs just after a ground strike, appears as a glowing sphere of various colours and can last up to 5 minutes ( http://www.eskimo.com/~billb/tesla/ballg... , http://www.abc.net.au/science/k2/moments... ). So far, it remains a mystery.

Come along now to The Science of Lightning, http://www.educ.uvic.ca/Faculty/mroth/43... , to find out what exactly happens when lightning strikes. During stage 1 in the formation of a lightning bolt ( http://www.educ.uvic.ca/Faculty/mroth/43... ), positive charge builds up on the top and negative charge on the bottom of rain clouds. Eventually, the negative charge (called a leader) begins to move towards ground taking a zigzag path (stage 2). During this time, the ground has been building up a positive charge, which begins to move upward (called a streamer). This is stage 3. When the negative charge meets the upwards moving positive charge, a completed circuit or channel is formed (stage 4). We now see the actual lightning bolt (stage 5). A return stroke travels up the channel releasing tremendous energy and light. The channel, once formed, can be used over and over again. Four or five strokes occurring with in a second gives the appearance of flickering. I thought lightning never struck twice in the same place?

Now you asked about a lightning rod? How does that work? I found a great web that explains the principle behind lightning rods-BBC Education's Benjamin Franklin and the Lightning Conductor, http://www.bbc.co.uk/history/programmes/... . Here we learn that a good conductor or lightning rod doesn't just stand there and get struck. It defuses the charge build up so that lightning doesn't strike at all. This is well illustrated in the "Lightning Game". Make sure you play it before leaving:-). (Also have a look at http://www.lightningrod.com/manual5_how.... ). Benjamin Franklin invented the lightning rod. Check out his biography, http://www.bbc.co.uk/history/programmes/... . You might like to try making a thunderstorm predictor, http://www.bbc.co.uk/science/scienceshac... , but be careful. Really an entertaining site.

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