Moon illusion


You may have heard about ‘moon illusion’, the way the full moon looks much larger when it is just over the horizon than when it is high in the sky. Many people will swear that it does actually appear larger and concoct theories as to why it is so, when the reality is that the larger size is a trick our brain plays on us, though there is no consensus on how it does it. In an earlier post I examined some of the explanations.

From reader Norm I received a time-lapse photograph of a full moon as it rises in the sky that shows conclusively that the size remains the same.

moonrise-timelapse-over-la

Comments

  1. Rob Grigjanis says

    From your earlier post;

    It [the Ponzo Illusion] depends crucially on the assumption that we have a mental image of the sky as a shallow dish.

    Surely that’s right. Think of days where there are clouds spread across the sky. If the shallow dish picture were false, such a day would appear quite odd, especially when the clouds are moving rapidly. It mirrors our perception of what’s going on under the horizon. We do seem to be symmetry-seekers.

    I haven’t looked into this, but the near-horizon moon appears smaller when it is bright. Is there science on bright objects appearing smaller?

  2. rq says

    Well, when you put all those moons next to each other like that, of course they’ll all look the same size!
    Lovely illustration of the illusion, thank you.

  3. StevoR : Free West Papua, free Tibet, let the Chagossians return! says

    @1. Rob Grigjanis :

    .. the near-horizon moon appears smaller when it is bright. Is there science on bright objects appearing smaller?

    Not sure or aware of any. I would however, expect it to be the other way around – that a brighter object would actually seem larger e.g. the hotter brighter desert sun often being portrayed as a larger star than the less bright (or perceived to be less bright) sun of cooler climes.

  4. jamessweet says

    I am a strong Ponzo partisan (I always forget the name of it, though, heh…). Unfortunately, it is a very difficult one to explain at parties, and I’m at “that guy” who will attempt exactly that 😀

    I like this photo, though. Very nice.

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