By Phil Plait | July 14, 2008 12:27 pm

I love illusions, as regular readers know. They play into astronomy as well into skepticism; you have to understand how your brain interprets images, or at least how it can be fooled, to correctly interpret astronomical imagery and antiscience claims (like pareidolia or cities on Mars).

I checked my blog archives, and incredibly I have never linked to Skytopia, a phenomenal collection of illusions. Well, I might have linked to it but I couldn’t find it, so it’s new to me, and maybe it is to you too. There are color illusions, geometric illusions, animated illusions, autokinetic illusions… it goes on and on. Go there, poke around, have fun, and exercise your optical nerve. How many examples are there that can be used to debunk antiscience claims?

CATEGORIZED UNDER: Cool stuff, Science, Skepticism

Comments (22)

  1. Craig

    <inserts tongue in cheek>

    Is that pronounced “sky-TOE-pia” or “sky-toe-PIA”?

  2. Wow, great link! I’ve been looking for something like this for a while now – and this is the jackpot.


  3. I really like the checkerboard shadow illusion. I saw a very similar one (probably linked to by you) at but this one is much stronger. I had to load it into my photo editor to prove it to myself. I grabbed a section of “square” B and dragged it off the board, and it got darker as I moved it!

  4. Viewer 3

    As long as they’re more impressive than that waste-of-time “audio illusion” you had a while back.

  5. Caleb

    One of my favorites:

    I know that A and B are the same shade (using a digital color dropper to compare the hex values), but no matter how many times I look at it, my mind tells me A and B are difference shades.

  6. MattGS

    Uh, I love illusions, too. Some of them are quite hard on the eyes though … they shouldn’t have put all of them on one page, I think.

  7. Oi. You goignto supply aspirin for that link, too? Still, it is way cool, :-)

  8. Funny you bring this up, Phil. I was getting ready to have my breakfast toast this morning, and this popped out…

  9. Kaptain K

    My head hurts!

  10. C Arnoldus

    Oh great, now I have a huge cyan dot in the middle of my field of vision.

  11. Michelle

    sweet! I love illusions! It’s so fun to… um, get a headache.

  12. Michelle

    …Okay you know what? that blind spot one just freaks me out.

  13. That “Eclipse of Mars was cool, but now I have a big glowing cyan spot in front of my eyes and can hardly see my keyboard.

  14. Blind spot is weird, which brings an astronomy question up: When looking at a star with the naked eye, why is it that if you turn your eyes slightly away, you will actually see it with more clarity, even being able to distinguish if it is actually a double star?

    I used to know tha answer to this, but I have forgotten.

  15. Another Eric

    Thanks a lot, now I can’t drive home for at least 15 minutes!!!

  16. A Real Climatologist

    Then you must love the illusion of globull warming. Stick to what you know best; astronomy. You know little about earth science.

  17. Brian

    Michael L: That’s because the color-sensitive cones are mostly jammed into a little circle at the center of your retina. The rest of the retina has a higher population of rods, which can only see in black-and-white but are more sensitive to faint amounts of light.

  18. madge

    Doh Brian beat me too it :)

  19. Wow, what for here sticked climate troll?

  20. CanadianLeigh

    Hi Brian, regarding Michael L’s question. I had noticed one exception to averted vision giving better vision at night and that is when I was trying to split doubles. They seem to blur together when you avert your vision. I finally understood why this happens when I read the article by Stephen James O’Meara in August’s issue of Astronomy. The article is titled Vanishing Acts, part 2. As splitting doubles is one of my fun pastimes when out observing, I found the article very interesting and instructive. As explained in greater detail in the article, direct vision will only work better if the stars are both bright enough and not to different in brightness. Before reading this article I just thought my eyes were getting too old.

  21. So, on the flip side of this, what causes the blind spot?

  22. Al

    The blind spot is where the optic nerve goes through the retina. As the nerve connections (also blood vessels) are situated in front of the light-sensitive cells, there is a gap in the coverage to accommodate them.


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