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Famous ‘moon footstep’ optical illusion shows the trick our brain plays

As Tom Stafford over at the always-interesting Mind Hacks blog demonstrates this week, our brains often play visual tricks on us. 

Here’s the famous photo of Buzz Aldrin’s footstep on the moon. Notice something strange — how the footstep appears to be rising out of the moon’s surface rather than being impressed into it?

Buzz Aldrin lunar footprint
Courtesy of NASA

“The effect,” explains Stafford, “is due to a well known visual phenomenon whereby our brains use shading to infer the perception of shape. We are wired to assume that light comes from above, so things with shading underneath, like the ridges of the footprint, are seen as sticking out towards us. Things with shading on the top are seen as sticking in, away from us.”

As Stafford notes, the optical illusion disappears when you turn the photo upside down because from this angle the photo “gels with our natural inclination to assume light comes from the top of the photo.”

Buzz Aldrin lunar footprint
Courtesy of NASA

Use this a reminder as you go into your weekend: Don’t believe everything you see — or, for that matter, read!

Comments (6)

  1. Submitted by Phil Dech on 10/16/2009 - 01:53 pm.

    I dunno. They both looked pressed in to me.

  2. Submitted by Joshua Abell on 10/16/2009 - 02:31 pm.

    I’m with Phil on this one. I’m not seeing it.

  3. Submitted by Dan Gerber on 10/17/2009 - 06:13 am.

    Weird. I don’t see it on the first photo, and
    can’t make it happen for me. But looking at the
    flipped photo, it “jumps out” after a few moments,
    and now I can’t see the flipped one correctly. I
    think the memory of having seen the correct one
    so many times as an impression in the dust has
    something to do with it for me.

  4. Submitted by Dan Gerber on 10/17/2009 - 06:26 am.

    If you look at the original (top) photo, the light
    is coming from the right at an angle, casting a deep
    shadow where the heel is. With the light coming from
    the same direction and angle on the flipped version,
    the heel seems to have broken off and fallen into the
    shadow.

  5. Submitted by jim hughes on 10/18/2009 - 08:54 pm.

    The illusion worked for me, right away. Interesting.

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