Ya know, I was just reading the topic on ball lightning and I really have to rant a little here. I saw a Discovery Channel or TLC show in the past year or so about lightning. They said that same thing about lightning “starting on the ground,” which I think is true in that there are tendrils (is that the right word?) which come up from the ground first–like the static-ish sparks you can barely see coming off a Van de Graaff generator.
Now, the thing that annoyed the hell out of me was when they claimed they actually captured a picture of the lighning starting on the ground with their cameras (they videotaped a staged lightning strike where model rockets with are sent up with thin wire to make lightning strike where a particular location.) They showed a freeze-frame of their video showing the lightning only in the bottom half of the picture.
This is stupid.
The area in frame was about 100 feet high. An electric spark crawling along through air at 0.1c is going at roughly 20,000 miles per second, so it would traverse the 100 feet in about 1 microsecond. The camera, in the mean time, is scanning one video field every 60th of a second, so basically they just demonstrated the scanning properties of the camera.
What actually happened is as follows. The camera was running, scanning a field at a time every 60th of a second, and (because of persistence of vision) making 30 frames per second. The camera would scan its imager from left-to-right, top-to-bottom in 1/60th of a second to make one full trip. In one of these fields, it made it about halfway down the imager when the lightning struck. All the air around the lightning spark started glowing within 1 millionth of a second between the top of the frame and the bottom. The camera continued on its merry way scanning its imager, but this time there was a big bolt of lightning right smack in the middle.
The resulting image looks like the camera captured half a frame-worth of a bolt of lightning.
My beef with this is that they didn’t realize what I said was the case. They had a bunch of videographers and scientists at their beck and call yet none were smart enough to know this. Ugh.
Not at all. Sounds like you hit the nail on the head. Unfortunately, TLC and Discovery seem to show a lot of hairbrained shows. (Try catching one on the paranormal. I can never decide whether to laugh or cry.)
Public television isn’t immune, either. When “Kratt’s Creatures” started, I caught a few episodes. I quit watching when I heard them pass along some misinformation on the animal kingdom a couple times. (Sorry, I don’t remember now what it was.)
I don’t know, NeedAHobby. Are you certain they said they used an ordinary video camera to record the raw images?
Besides a full-frame video camera (which do exist), there are also high-speed motion picture cameras that might have done the job. Recall that you’re not actually seeing “electricity” traveling at some significant portion of c, but the glow from the ionization of the surrounding air, which probably lasts longer than the bolt itself.
On the other hand, the people involved might have been as ignorant as you suggest. Considering the embarrassingly large percentage of air time TLC and Discovery dedicate to utter stupidity such as UFOs and the paranormal (as MrKnowItAll points out), I certainly wouldn’t put it past them.
But I probably shouldn’t single out particular networks: I wouldn’t trust any of them to provide truly accurate and unbiased information on any subject!
I’ve seen the show several times. It’s head and shoulders above most of the “raging planet” type shows; there is genuine factual information given along with some pretty good graphics, and just enough noise and dramatic music to keep students attentive (I’ve shown it in class once, and it stimulated a lot of discussion).
I know the photo you’re talking about, Need. And it is a photo, not a film or video frame. And it’s not from the segment showing induced strikes in New Mexico. It’s a time-exposure photo of a bolt striking a pine tree. About 100 yards away there is a utility pole. Extended above the pole you can just make out an ionized streamer the pole was sending upward, too late to close the circuit with the cloud. I’ve got a slide of it, unfortunately it is copyrighted and I can’t post it here.
The problem is that reasonably good show like this will be surrounded by an hour of tornado videos that don’t even attempt to provide information about the phenomenon, and a show about UFO phenomena that (if we’re lucky) will debunk the phony claims, films, and pictures in the last five minutes.
First, ambushed: I don’t think it matters if they used a high speed camera. Even that, taking say an incredible 1,000 frames per second wouldn’t capture half a bolt–remember that it takes only 1 microsecond to travel the height of the frame, so that’s still 1,000 times faster. Besides, the camera has a mechanical shutter which presumably sweeps vertically across the frame as it’s opened and closed. One millisecond per frame means the shutter is probably open less than half that time, but it’s still not fast enough.
To make matters worse, I hadn’t even thought through the ionizing of the air. This makes it impossible to capturing half a bolt of lightning. The air ionizes over the course of tenths of milliseconds (I’m just guessing) which then allows the electricity to conduct across it. It’s not like it ionizes in the path of the electricity, as say a bullet would make a wavefront, so there’s really no way to capture a path of air where part of it is ionized and full of electricity travelling quickly in a direction.
Second, jrepka: I know the photo you’re speaking of. I can’t imagine they wouldn’t show that picture during the program, but they actually used a camera and went through the footage frame by frame, stopping at the miraculous “half-a-bolt” frame.
We could expand this to include the things we learned in grade/high school that were blatently wrong.
My first one- Thomas Edison was responsible for the electrization(word?) of America. Edison steadfastly refused to use the AC system, believing DC to be superior. Actually, Tesla’s designs were used by Westinghouse to develop the AC system we use today. And we can leave out the obvious one about Columbus proving to Europe that the world was round by “discovering” America.
That one is too easy.
One of my favorite scientific urban legends is Ben Franklin’s kite was hit by lightning, or even better, that Ben “invented” electricity. It wasn’t and he didn’t.
reported to be from a 6th grade history test:
Delegates from the original 13 states formed the Contented Congress. Thomas Jefferson, a Virgin, and Benjamin Franklin were two singers of the Declaration of Independence. Franklin discovered electricity by rubbing two cats backwards and declared, “A horse divided against itself cannot stand.” Franklin died in 1790 and is still dead.
Keep in mind we’re talking educational television. TV was invented so you can look at the pretty pictures. If you want genuine knowledge, go read a book.
NeedAHobby: First, I think the ionization question can come down on either side of this. My guess (and that’s all it is) would be that the visible ionization “trail” lasts much longer than the bolt itself. It seems like this would permit a slower-speed camera to be used.
Speaking of camera speeds: you might be surprised to learn that there are video cameras that can record several thousand full frames per second! In split-frame mode, some video systems allow up to twelve thousand!
If that’s not fast enough, film’s your best bet. Many high-speed motion picture cameras do not use a traditional shutter precisely for the reasons you point out. There are commercial high-speed MP cameras that can record eleven thousand fps – and 44,000 quarter frames per second! This gives you a quarter frame time of less than 25 microseconds, which seems plenty fast enough to me.
If it’s not, there are MP cameras with an “effective shutter speed” of one millionth of a second!
Still not fast enough? Ultra-high speed photography gets you down to nanosecond or even picosecond speeds!
So I hope we can agree that it’s not impossible to have recorded an upward streamer. The question again comes down to did they.
If you’re upset about TLC getting lightning wrong, we’d better not even start on their never-ending series of shows spouting Bauval and Hancock’s nonsense about the Sphynx and the Pyramids.
It is fairly common knowledge (at least for engineers that work with High Power transmitters like TV and FM stations) that lightning almost always starts from the cloud (called a ‘leader stroke’) and heads for the ground. Before it reaches the ground, however, a counter stroke starts upward. The two ends of the stroke meet approximately 1/3 of the way up from the ground. This is fairly easy to prove using a 35 mm camera, a tripod, and some ASA 200 film. Set the iris wide open and in manual mode. Open the iris and then quickly pan back and forth across an area of the sky where lighting is firing. As soon as you think you caught a stroke on the film, close the iris advance the film and try it again until you use up the roll. Then process and print the usual way. Your prints will show you that each lighting stroke is actually anywhere from 15 to 30 very rapid stikes. Panning the camera rapidly creates individual images of each of the discrete stokes. Contrary to the old “lightning never strikes twice in the same place” lightning is actually more likely to strike the same place again during a storm. A single flash you see with your eyes is actually about 20 very rapid strikes to the same point. Sometimes the upward leading stroke fails to connect and you can see it clearly standing on it own.
I’ve used the above technique to study the behavior of lightning and have actually managed to catch the partial leader rising toward the cloud.
I’m not sure that the scan rate of a standard NTSC type camera is capable of the speed necessary to capture a portion of the stroke. The gentleman who broke it down into discrete time is correct. The video scan rate can’t keep up with the speed of a lightning strike but a slow motion video diplay (shot at 30 fps) could create the illusion that the stroke is moving up. It really does, but . . .
A great place to read more about how high voltage works is at the Tesla Research Center. http://www.ttr.com/
I didn’t realize people could take pictures that fast. I really doubt this show had the budget to have one of them there “fancy” cameras. (sorry, drawling again) By the way, I’m pretty sure the ultra-high speed photography in the nanosecond to picosecond is done with slower shutter speeds and high-speed flash units.
As for the ionization, I think it would make it impossible to capture part of a lightning bolt (not the leaders). I think the writers on the show were confusing two things: “motion” of electricity and leaders that start on the ground.
I believe lightning works as Sensei described, and I’ve seen photos of leaders and such. However, leaders are not the white-hot bolt you generally think of when you talk about a lightning strike. The image I saw on TV was a white-hot strike about 50 to 100 feet long which was touching the ground but didn’t go off frame. I believe this was the full-blown lightning strike and not a leader.
The point of this post is that I think it’s impossible to catch a picture of a partial lignthing strike (the full bolt instead of a leader). It’s because you’re looking at the ionized air, not the electricity itself. This is how I believe we see a lightning strike:
Over the course of several milliseconds, the air starts to get ionized enough to seriously conduct electricity, forming a leader. The discharge itself travels 100 feet in a microsecond across the leader, and over the next 10 to 100 microseconds the electric current increases, the air ionizes more, and it emits the bright white light we see as a lightning strike.
Based on this, I don’t think it’s possible to capture half a bolt of lightning. Although it may be possible to take a picture fast enough to split up the start of the electrical discharge, it’s not until “much later” (i.e. dozens of microseconds) that the white-hot flash is fully visible–this ionization gradually increases in brighness over dozens of microseconds and doesn’t appear to travel either up or down.