Don’t believe your eyes.
Optical illusions, experiments to try at home and printable puzzles for curious people of all ages. Every fact here links to its source. Start with the game: can you name the trick from one clue?
Which illusion?
8 clues. Pick the illusion or device each one describes.
Press start for your first clue.
Ten kinds of trick
- Size illusion
- Impossible object
- Ambiguous figure
- Pareidolia
- Stereoscope
- Camera obscura
- Zoetrope
- Afterimage
- Colour and shade
- Op art
Each clue in the game is one of the facts in the illusion file. After you pick, the full fact and its source appear. The drawing above is our own: the two lines are the same length, the two squares of the cube are the same size, and the middle circle is just a circle.
What is illusions.im?
illusions.im is a small hub about optical illusions: what you see, why your brain gets it wrong, and how to make the tricks yourself. Each kind of illusion will get its own site with sourced facts, experiments, games and printables. Some true things to start with:
The same, honestly
In Ted Adelson’s checker shadow illusion, a square in shadow and a square in the light look very different but are exactly the same shade. [source]
Pinky test
Test the moon illusion yourself: at arm’s length, about two-thirds of your little finger covers the moon, however high or low it is. [source]
A face on Mars
In 1976 a Viking orbiter photographed a rock formation on Mars, in the Cydonia region, that looked like a face. In April 1998, after a public outcry, the Mars Global Surveyor was programmed to photograph it again. [source]
Blame Bristol
The café wall illusion was first reported by Richard Gregory and Priscilla Heard in 1979, after one of Gregory’s team noticed the tiled front of a café on St Michael’s Hill in Bristol. [source]
Coming soon
Ten illusion sites are planned. The two marked “First wave” come first.
- Size illusionsFirst wave
size-illusions.illusions.imPlanned: equal lines that look unequal, circles that grow and shrink, the moon on the horizon, and how to measure each trick with a ruler.
Coming soon - Impossible objectsFirst wave
impossible-objects.illusions.imPlanned: shapes that can be drawn but never built, the devil’s fork, step-by-step drawing guides and where the idea came from.
Coming soon - Ambiguous figures
ambiguous-figures.illusions.imPlanned: one picture, two answers. The vase and the faces, the flipping wire cube and the hollow face that won’t stay hollow.
Coming soon - Pareidolia
pareidolia.illusions.imPlanned: faces in clouds, plugs and rocks, the “face” on Mars, and why the brain is so quick to see faces everywhere.
Coming soon - Stereograms
stereograms.illusions.imPlanned: how two flat pictures make one solid one, the Victorian stereoscope craze, and making your own 3D pictures.
Coming soon - Camera obscura
camera-obscura.illusions.imPlanned: the “dark chamber” that turns the world upside down, building a pinhole viewer, and the ancestor of the camera.
Coming soon - Moving pictures
moving-pictures.illusions.imPlanned: zoetropes, flip books and spinning toys, the phi phenomenon, and why wheels on screen spin backwards.
Coming soon - Afterimages
afterimages.illusions.imPlanned: colours that appear after you look away, the green dot that isn’t there, and dots that fade while you stare.
Coming soon - Colour and shade
colour-illusions.illusions.imPlanned: two identical greys that look different, colours from a black-and-white spinning top, and grids with ghostly spots.
Coming soon - Op art
op-art.illusions.imPlanned: the art movement built on optical illusion, the café wall, and patterns that seem to move and shimmer.
Coming soon
Sister hubs
illusions.im is part of the same REALLYBYTE family as these hubs:
Enjoyed the tricks?
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