Square Circle Spiral

Bad Astronomy
The entire universe in blog form
Aug. 18 2009 5:02 PM

Square Circle Spiral


One thing I love about having cool friends like psychologist Richard Wiseman: I see all kinds of things I never would have otherwise. On his blog Richard posted one of the best optical illusions I have ever seen:

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

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square circle spiral illusion

Oh baby! Let your eyes roam over it; the squares appear to form a spiral pattern. But then more carefully trace over the pattern -- block some of it with your hand to be sure -- and you see they are aligned in perfect circles.

Still not sure? Let me prove it: all I did was draw in circles.

Square circles annotated

Even with the circles right on top of them it's hard to see the squares laid out in anything other than spirals.

Incredible.

I love illusions like this, ones that persist even after you can see the trick. And as always, I like to point out that when someone swears they saw something and then say "Seeing is believing," you can point them to things like this and say, "Not always." Remember: it's easy to be fooled, especially when you're not expecting it.

Richard posted a couple of other illusions on his blog, so go look. Also, you can follow him on Twitter!