Start of Lightning Bolt Caught on Camera | Hacker News Reader

Start of Lightning Bolt Caught on Camera

realclearscience.com

224 pointslelf35 comments

Great video, the nature article is much more informative than the one linked.

From the nature article, it seems this was the first video of natural bidirectional lightning, not triggered by rockets or aircraft: "In contrast to studies of rocket-triggered lightning and lightning initiated by aircraft, which found delays of 3–6 ms between the onset of negative and positive leader branches, this natural event exhibited a delay of less than 90 μs (i.e. one video image)."

This was a negative polarity lightning strike. the most common type. Less than 5% of lightning is positive polarity but they can carry ten times the charge and exceed a billion volts of potential.

When you read about people surviving lightning strikes it's almost certainly a negative polarity strike. https://en.wikipedia.org/wiki/Lightning#Positive_and_negativ...

Are the positive ones the "bigger" ones?

EDIT: From the linked Wikipedia entry: "Because of the much greater distance to ground, the positively charged region can develop considerably larger levels of charge and voltages than the negative charge regions in the lower part of the cloud."

I didn't know about positive/negative polarity types of discharges, thanks!

Also, having Cloud to Butt extension installed made reading that Wikipedia quote quite interesting...

...carry ten times the charge and exceed a billion volts of potential.

Great Scott!

I also like this 10,000 fps video [0] credited to Tim Samaras.

[0] https://i.imgur.com/W1X1qFI.jpg

I was wondering how you could talk about a video and then link to a single image (I think jpg doesn't support animation). But it turns out all of

https://i.imgur.com/W1X1qFI.jpg

https://i.imgur.com/W1X1qFI.gif

https://i.imgur.com/W1X1qFI.png

link to the same GIF. :)

Ah good thing, so imgur abstracts extensions apparently

Better if you request with .gifv extension, then it's a much smaller (than a gif) html5 video)

The only issue with gifv is that if you open one on iOS it will pause whatever music you're listening to at the time. Kind of a bummer and something that will hopefully eventually get fixed.

I think that makes sense as I believe in their system the identifier will be

W1X1qFI which happens to be the url/filename and is auto-generated it ignores the extension

instead of throwing a 404.

For a second there I though they'd done something really clever with progressive jpegs!

Here is the Nature article that this video goes with. http://www.nature.com/articles/srep15180 .

That's obviously more substantive, and HN prefers original sources, but unfortunately it doesn't include a link to the video, so I guess we'll leave the URL as is.

It is unfortunately hidden at the bottom as .mov in the supplementary information section: http://www.nature.com/articles/srep15180#supplementary-infor... .

11k fps. Wow. I will never get tired of watching this stuff.

That got me thinking, is there any theoretical limit to the number of frames that can be captured in one second?

"Single-shot compressed ultrafast photography at one hundred billion frames per second" - http://www.cnet.com/news/worlds-fastest-2d-camera-can-captur...

Here is a pretty good video at a trillion frames per second: https://www.ted.com/talks/ramesh_raskar_a_camera_that_takes_...

The cameras doing a billion+ frames/sec do not really function the way traditional cameras do -- i.e. you could never use one to take a picture of lightning (which is a pity). They work by firing off billions of extremely short bursts of laser light, and capturing images at progressively longer offsets from the release of a pulse. That strobing light is an integral part of how those cameras work, so they can only be used in situations where you can control the illumination of the object.

(Which does not make that technology, mind you, any less cool. But it's different enough from traditional photography that I thought it was worth mentioning.)

Electricity travels at about one third the speed of light. That would make a hard limit. Both shutter and data transfer speed.

But that would just be for one recording device. If you could use multiple devices, perhaps with small POV differences that could be corrected, I would expect no limit in that "lossy" case.

But if you surrounded an event with a sphere of sensors, there is still an upper limit. The number of sensors is a function of sphere radius, and whether they are limited to the surface of the sphere (which is reasonable since tightly packed sensors will, in general, get in the way of other sensors).

A sphere 1km across has a surface are of 4pi1km^2 which is roughly 10^7m^2. If you had 1cm^2 sensors then you get 10^4 sensors per m^2, which means you get 10^11 sensors total. At 11k fps (10^4) that's a total of 10^15 fps.

Note that Planck time is 10^-44 so such an arrangement probably wouldn't help for detecting quantum gravity because you'd run out of matter in the universe before you could construct the sensors.

It is not clear how one would synchronize the cameras on such fine time scales either.

Amount of total photons emitted or hitting the Planck limit, whichever comes first.

POV differences could be eliminated by a simple lens & mirror setup.

Ultimately, sure, you run out of photons.

Let's start off with a baseline image resolution of 1 megapixel.

1 Joule is about 6E18 visible light photons, give or take. So that's then 6E12 photons per pixel.

Full sunlight on Earth has an intensity of around 1400 Watts (Joules/second) per square meter, or 0.14 Watts per square cm.

So achieving a frame rate in the trillions of fps would likely run into some limits relative to the size of your optics, the intensity of light coming from the scene, or the bulk quantum efficiency of the sensor.

And, of course, if you try to achieve quintillions of fps then you start dumping in nearly an entire Watt in photons into every single pixel on your sensor, which rapidly becomes a very big problem re: everything melting.

Additionally, modern electronics has trouble operating above the low GHz range, beyond that you'd need to move to superconductors or some such to keep up with the data.

The number of captured photons is a good hard limit. dalke's answer for ultrafast photography is kind of "cheating" in the sense that they record the same event periodically so they can gather enough light. That technique can't record single unique events that fast AFAIK.

No, it's not "cheating."

The title of my link says 'single-shot'. The underlying Nature article at http://www.nature.com/nature/journal/v516/n7529/full/nature1... says "Here we demonstrate a two-dimensional dynamic imaging technique, compressed ultrafast photography (CUP), which can capture non-repetitive time-evolving events at up to 10^11 frames per second"

Not that it isn't awesome how fast cameras are, just keep in mind, the clip is 25ms. So at 11,000 fps, that would be 275 images (11 frames per ms). Not sure if we actually have a camera that can take 11,000 images in 1 second. (I guess that depends on the resolution)

We do have those, but it does indeed depend on the resolution.

These can do 25k fps at 1280x800 pixels (and 1 million fps at 128x32 pixels): http://www.visionresearch.com/Products/High-Speed-Cameras/UH...

Yeah we do. The company I work for designs sensors that can pull that off.

lightning is enigmatic

and the internet facing community surrounding its research seems divisive

can anyone speak to the sort of research currently being done on the study of lightning and its initiation?

are there efforts to recreate assumed initial conditions?

thoughts on the source of the huge amounts of directed energy? does the strike harvest from the vast collection of charged particles within the cloud or is it created by electrostatic interaction of individual ions, similar to http://www.nature.com/nchem/journal/v7/n3/full/nchem.2161.ht...?

Site down.

Direct link to the video: https://www.youtube.com/watch?v=4dwBS9nLPbE

Thanks. Seems to be back now.

a) overloaded site

b) very nice, but is this "Hacker" News? More like Discovery Channel. How is this interesting from a tech point of view? High FPS cameras. Got it. Got it long ago.

"High FPS Camera" is a lot more impressive than the latest twitter-controlled todo-list app or whatever.

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