>> ^messenger:

If this is the real deal, then how come I can see the sun through the "planet"? Aren't planets opaque?

Lens flare - the sun happens to be rather bright! Is also very likely to be residual afterimages on the sensor - it's hard to properly handle the vast amounts of light involved.

I took a couple of images myself with my SLR - had I not used three layers of ND-filters as well as post-processed the Raw files, I would have had to use shutter speeds of about 1/8000000th of a second - a thousand times faster than my camera is capable of.

...some cropped web page....

Let's take a look at the process through which lightning is known to be formed. Lightning occurs because of a difference in charge between a storm cloud and the ground.

First, the base of a cloud sends down a little electric discharge, called a stepped leader. It descends to the ground in steps, each about 50 yards (about 46 meters) in length. This process is extremely fast and impossible to see with the naked eye. Each step is less than a millionth of a second long. The interval between steps works out to about fifty-millionths of a second. This process can only be observed with the assistance of extremely quick-exposure cameras.

The stepped leader generally moves at about 75 miles per second (120 km/s) towards the ground. A typical trip duration is 20 milliseconds. Atoms pass along electrical charge much more quickly than sound vibrations.

The stepped leader carries tons of negative charge. As it nears the ground, it induces enormous quantities of positive charge in the earth, especially at the tips of tall objects. Because opposites attract, the stepped leader and the negative charge at the ground reach towards each other and quickly meet. The path from storm cloud to the surface is complete and "the floodgates are open", so to speak.

Because the cloud is filled with negative charge, it has a lot of current to offer to the newly created discharge path. This charge quickly moves from being distributed throughout the cloud to being concentrated at the point where the stepped leader first dropped from the cloud, into the ground or an elevated object. This discharge is called the return stroke, and is what we think of when we hear the word "lightning".

The return stroke takes around 100 millionths of a second to reach the ground. The immense flash generated is enough to leave an afterimage in our eyes for seconds at a time, giving us the illusion that the lightning flash is longer than it really is. In reality, our eyes cannot resolve any of the steps involved. We only see the final product - a lightning bolt.

>> ^Mcboinkens:

Why do I not understand how this works.


"Persistence of vision is the phenomenon of the eye by which an afterimage is thought to persist for approximately one twenty-fifth of a second on the retina."

Eadweard Muybridge is considered the father of filmmaking for his first attempts at capturing this phenomenon with his Zoopraxiscope. Who says film students aren't worth something?

In the vid above they just talked about the anatomy of the retina.

... and they kind of get it wrong, specifically because they refer to 'afterimages' when talking about persistence of vision theory, and then act as if the 'reseting period of the eye' is all rod and cone cells firing in unison at a framerate or something, and our brain is filling in the gaps of this constant full retinal reset (nothing like this happens).

'Afterimage' is caused by fatigued cells that have been overstimulated, made to release more neurotransmiter than they can replace. You stare at something red, then look at a white piece of paper (which stimulates all 3 cone cell varieties), and the red object from before appears as a green afterimage on the paper because the cones in the red wavelength are tired. This castle post was an 'afterimage' demo - http://www.videosift.com/story.php?id=3783

Persistence of vision is very complicated; depends on amounts of spatial displacement between frames, amount of time between frames, amount of stuff in the frame,... its weird. The brain sees this and decides whether it sees motion or whether it sees jerkiness. Talking about the brain skipping over black spaces when watching a movie projection is strange; its not like we have photoreceptors for black, so theres just nothing to see...

I'm glad this group employs some talented drumline guys. It sucks they don't employ any neuroscientists, though ; )

Try it with one eye closed - if you close the eye that sees the color image (it's an afterimage - what you are staring at until the change is a negative) and quickly open the other eye, the image will be in black and white. You can alternate eyes for a couple of seconds to "blink" the color on and off.

If the color disappears then re-focus on the black dot in the black and white image. The color suddenly reappears when I do that. It's as though my brain filters out the afterimage unless it's perfectly aligned with the black and white one.