Man, I used to think optical illusions were the simple, “which line is longer” sort. But I have seen some optical illusions in the past decade or so that have really caused me pause. It’s like there’s been some sort of optical illusion renaissance recently.
Here is one of the animated variety that wouldn’t have worked presented, as they were when I was young, in book form. Wow.
Okay, I was curious, what is a “gabor element”? It turns out the “Gabor filter” has an interesting mathematical (and even biological) origin.
For the creative, there is a nice online tool allowing you to create a gabor element here. It should be possible to generate a series of them out of phase and stack them with a GIF-creation tool in order to experiment with you own illusions similar to the above.
When I was a teenager I had a friend who showed me one of the oddest things I had seen. In a drawer, he revealed this frightening looking thing that you see to the right. His older brother was in the U.S. Navy and, my friend said, his older brother had come back from some distant port with this oddity — some sort of sea devil.
I thought I was witnessing some sort of real-life Ripley’s Believe It Or Not side-show in his bedroom that afternoon. What the hell was I looking at?
Years later, when I recalled that bizarre brush with cryptozoology, I set about searching the Web, trying to find out what it was I had seen. And that is when, at last, I came to find that these mer-creatures are referred to as “Jenny Hanivers“.
There’s a long discussion of the lexical origin of the name on Wikipedia if you are interested.
If you have a penchant for the unusual, search eBay for “Jenny Haniver” and pick one of these monsters up for yourself.
Probably at some point you have seen the way some animal’s eyes sort of light up when a car’s headlights have swept past. Perhaps it was a neighborhood cat in the night or maybe a coyote, but when the light shined in their face you saw a bright glow from their eyes.
That glow is of course the light of the headlights reflecting back at you. A thing that has that reflective characteristic is called a retroreflector. In this case the retroreflector is the animal’s eyes.
Another retroreflector you’re familiar with is the bicycle reflector. If you’ve ever looked at one very closely you will see the surface of the reflector is composed of many, many small pyramid shapes. These are positioned and angled such that they bounce any light shone at them straight back at its source.
A retroreflector you may not have heard of is one that went with the astronauts to the moon on an Apollo mission. It was left on the surface of the moon pointing earthward. In this way, engineers on Earth were able to shine a laser at it from these thousand of miles away and have that laser reflected directly back. By timing very precisely the length of time it took the laser to travel to the moon and back, we now know the distance to the moon to within a few centimeters.
But now here’s where it gets maybe a little creepy. Did you know that spiders have remarkably retroreflective eyes? If you take a flashlight and go out at night in an area known to have spiders you will see their eyes reflecting very brightly back at you. The only trick to doing this is to make sure the flashlight is held as closely to in-line with your eyes as you can. That is, you want your eyes right behind the flashlight so that you see the light from the spider’s eyes that is being reflected straight back at the flashlight.
Below: Some folks showing you how to find spiders in the night with a flashlight.