Visual Tricks & Treats From Inq's Stereoscope

Visual Tricks & Treats From Inq's Stereoscope

Reel 1: A Tour of the Solar System

Your first stereo reel is a curated tour of  the solar system, from the Sun to the minor planet Arrokoth, the farthest object ever explored by humans. It’s a trip of 6.7 billion kilometers you get to make from the comfort of your own home!

Slide 1: Solar flare and spicule

The first two images are from NASA’s Solar TErrestrial RElations Observatory (STEREO) mission, a unique solar observatory that consists of two identical spacecraft that provide the proper binocular disparity to create 3D solar images. The STEREO-A spacecraft is located ahead of the Earth, leading it in orbit around the Sun; and provides the “right eye” perspective.  STEREO-B is located behind the Earth, following the Earth in orbit and providing the “left eye” perspective (the “A” stands for “ahead” and the “B” for “behind”).

This image from STEREO’s Extreme Ultraviolet Imaging Telescope was taken on March 17, 2007; the green is a false-color added for clarity, showing the area of the Sun’s atmosphere that is at 1.5 million℃. The feathery structure you see is a “spicule” - a burst of gas that explodes off the Sun’s surface - that stretches up to 10,000 km, then collapses. As many as 10 million of them are erupting at any given time!

Slide 2: Solar prominence

Your second image taken by the STEREO mission, this slide shows a solar prominence erupting from the left limb of the Sun’s north pole on March 20, 2007.

Prominences are eruptions of plasma from the Sun’s surface that extend into it’s corona; they flow along a twisted structure of magnetic fields that are generated in the Sun’s interior.  A typical solar prominence reaches a height of 100,000 km, almost ten times the diameter of the Earth! The red false color shows the features of the Sun that appear around 80,000℃.

Slide 3: Ares Vallis floodplain, Mars

This photo taken by the Mars Pathfinder spacecraft shows its landing site on the Ares Vallis floodplain, including the airbags and solar petal of the craft itself. Ares Vallis is an outflood site, carved by rivers of liquid (probably water) during a warmer period in Mars’ past.

The airbags are part of Pathfinder’s amazing landing system: it involved supersonic parachutes and a cocoon of airbags that blew open and enveloped the craft about ⅓ km (1,000 feet) above the surface. Upon impact, the airbags caused Pathfinder to bounce 15 meters (50 feet)  back into the air like a superball! It bounced about 15 more times before settling on the landing site. 

Slide 4: Pooh Bear rock and Mermaid Dune, Mars

This photo was taken by the Pathfinder mission’s Sojourner Rover on the Ares Vallis floodplain. The large rock on the left is called Pooh Bear, and the smooth area stretching across the top of the image is the Mermaid Dune. Many of the rocks at the Pathfinder landing site are named after cartoon characters: in addition to Pooh Bear, other formations are Piglet, Scooby Doo, Stimpy, and Yogi!

Slide 5: Comet 67p dust jet eruption

Here’s some good news: you may get to see this comet live, in just a month! The downside: you’ll need at least an 8-inch telescope to do it, so check with your local astronomy club. Comet 67p, also known as Churyumov-Gerasimenko, has an orbit of 6.45 years, and it’s next closest approach to Earth will be on November 12, 2021. 69p is the first comet humans ever landed on: in 2014, the ESA’s Philae robot lander dropped from the Rosetta spacecraft and touched down on its surface.  

This image shows typical (and dramatic!) cometary behavior: as they near the sun, comets start to melt, causing them to blast gas and dust off into space. How much do they melt? Comet 69p loses about 1 meter of thickness with each orbit. The smaller lobe has a diameter of over 2 km, and will completely evaporate in a few thousand years. 

Churyumov-Gerasimenko is a “Jupiter Family” comet, and its orbit loops around the Sun, crossing the orbits of Jupiter and Mars; but it doesn’t cross Earth’s orbit - right now. Its orbit has shifted significantly over the last few centuries. Before 1840, the closest it got to the sun was 4 AU, which wasn’t close enough to melt any of its ice - meaning the comet had no tail, and wasn’t visible from Earth. Passing by Jupiter in 1840 altered its orbit enough to bring it even closer to the sun, at 3 AU. Further orbits brought it ever closer, and by 1959, it was orbiting at just 1.3 AU from the sun. In 2220, it will cross Earth’s orbit, at just .8 AU.

Why does it have two names? 67p means it was the 67th periodic comet to be discovered, and the people who discovered it were Soviet astronomers Klim Churyumov and Svetlana Gerasimenko.

Slide 6: Pluto


The largest of the Trans-Neptunian Objects, Pluto was once thought to be a bland, featureless world; but NASA’s New Horizons spacecraft showed it had mountains, craters, glaciers...and red snow. This image was taken by New Horizons in 2015.  

The scarlet plain you see on the bottom left is the Cthulhu Macula, an area covered by reddish tholins that fall from the sky like snow (and yes, named after H.P. Lovecraft’s Cthulhu). On the right, you’ve got the heart-shaped Tombaugh Regio; the left half of the heart is a giant glacier of frozen nitrogen.

Slide 7: Arrokoth

The end of our tour leads to distant Arrokoth, the farthest object yet visited by a human spacecraft: NASA’s New Horizons flew past it in 2019, four years after encountering Pluto. Arrokoth is the word for “sky” in the Powhatan/Algonquian language; prior to its official naming, the object was known as Ultima Thule. The minor planet is about 36 kilometers long.

Arrokoth is extremely distant: 6.6 billion kilometers from Earth (and 1.6 billion kilometers past Pluto). It orbits the sun once every 293 Earth years and has an unusual shape from being a “contact binary” - meaning that it was once two objects until gravity pulled them ever closer, finally smooshing them together. 


Reel 2: Binocular Optical Illusions

One of the cool things about the stereoscope is that it allows you to explore unusual illusions, taking advantage of the stereoscopic effect by showing each eye a separate image. Without that optical separation, most of these effects cannot be experienced in everyday life.

Slides 1 & 2: Impossible colors

The first two slides are “impossible colors.” These are colors that don’t in a sense really exist, because your brain can’t normally process them. Why not? What we perceive as colors are wavelengths of light received by the cone cells in your eyes. The brain then combines the millions of signals from your cones and creates a composite image of the color you’re seeing. So in a sense colors don’t exist, only the perception of them that our brains put together.

But here’s the weird part: the neural cells that register those signals can only process one color at a time; some of them are blue or yellow, and some of them process red or green. When you look at a green image, the green portion of that neuron is stimulated and the red portion inhibited. So your brain literally can’t normally register a color that is equally red and green, or equally blue and yellow (there’s also a good explanation of this on pages 75-76 of your new Blue: In Search of Nature’s Rarest Color book). But experiments in the early 1980s showed that if you can show each eye, completely separately, the opposing colors, the brain combines them into the so-called “impossible” colors.

To make these slides work, stare at the cross in the center of each one; your brain will produce the impossible color. One important note for best results: the colors entering each eye should be the same luminance, so try and use a stable light source that shines equally brightly into both eyepieces.

Slides 3, 4, & 5: Binocular Rivalry

The third, fourth, and fifth slides on this reel explore the phenomenon of “binocular rivalry.”  Normally, each of your eyes sees a very similar, but slightly different image, and the brain puts them together into one single picture. Binocular rivalry happens when the eyes present the brain with two images that are so different from each other that it can’t merge them into one image. Instead, your perceptual experience will alternate between the images. For example, in slide 3, you’ll start off seeing a person’s face, then after a few seconds, it will switch and you’ll be looking at a building. The time between switches changes randomly, but it’s generally every 3-4 seconds.

Neuroscientists use binocular rivalry experiments to investigate perceptual conundrums, including:

  1. The locus of awareness: at what stage of perception the brain’s experience correlates to your conscious experience
  2. Perceptual selection: how the brain resolves competition between two images and decided which one to bring to awareness
  3. Unconscious processing: which parts of an image that are suppressed from awareness but are still processed

Slides 6 & 7: 3D afterimage

For this illusion, we’ve presented a negatively inverted 3D image of the Earth. By staring at the dot in the middle for about 30 seconds, and then clicking to the next slide (the blank one), you should see a regular, positive color 3D afterimage of our home planet.

Afterimages occur because when light enters your eye, it produces chemical changes in the photosensitive cells called rods and cones. If you stare at the same thing for too long, the chemicals can get temporarily “exhausted,” desensitizing the cells to the color they’ve just been staring at. When looking at a neutral background, the other, fresher cells nearby send a nice bright input, while the exhausted ones send only a weak signal, and you see the reverse of the image you’ve been staring at - the afterimage.

Focusing on that dot in the middle of the image is important to making those photoreceptors tired. That’s because your eyes normally have tiny little jittery movements called “saccades,” to prevent them from becoming fatigued when staring at the same place for too long. Focusing on the dot in the center reduces the saccades, allowing those photoreceptors to get tired, and the afterimage to appear!

That’s why so many optical illusions have focus points in the center; your eye is pretty good at avoiding the types of tricks that cause these illusions, and the saccades are a big part of that.

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