According to the Wikipedia article Moon illusion, it has apparently been "proven" that the moon's larger appearance at the horizon is, indeed, an illusion, and not a magnification of some kind.

I think we can accept this proof, since (as pointed out by the comments and the Wikipedia article) there are several very straightforward ways to verify this.

In spite of this, there is still disagreement about what causes this illusion.

So what is the real reason? A quick Google search pulls up a few articles like this one that tend to rely entirely on their own explanation on not on any studies or external evidence whatsoever.

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    Take two pictures: one of the moon high in the sky and one of the moon setting. Use the same zoom level. Will the picture of the moon have the same size? (hint: yes). :-)
    – Sklivvz
    Commented Mar 26, 2011 at 21:34
  • Hey, the Astronomy StackExchange also covered this: astronomy.stackexchange.com/questions/183/…
    – JasonR
    Commented Oct 28, 2011 at 15:43
  • To my eyes, the moon looks the same size on the horizon as it does when it is in the sky. I can vaguely recall that when I was very young it looked bigger, but it does not now, even if I try to trick myself into thinking that it does.
    – Michael
    Commented Jun 21, 2014 at 4:36
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    I think this question is actually off topic for this stack. Asking if the moon bigger on the horizon then overhead, is an easily verifiable fact but borderline on topic, as it's a truth-claim. Asking if a specific explanation is correct should also be (again, borderline) on topic. But asking for an explanation in general, belongs squarely on another stack, such as Astronomy.
    – SQB
    Commented Feb 22, 2017 at 12:10

1 Answer 1


enter image description here

(Image comes from http://www.moillusions.com/2008/12/moon-optical-illusion.html and may have nothing to do with the 'real' moon illusion.)

Donald E. Simanek has a very good article about the phenomenon on his website. The opinion presented in his article is that the true nature of the illusion is not completely understood. He presents a number of theories, debunking those that are wrong, and offering suggestions about the more plausible ones.

For the time being, the whole true reason behind the phenomenon remains unresolved.

Update: One of the links was reported to be broken. The original link is left unchanged, in case the broken link becomes repaired, and a new link to the Donald E. Simanek moon illusion article has been added.

  • Good answer, thank you! This is the type of answer I like to see here, with links and even illustrations.
    – Nicole
    Commented Mar 26, 2011 at 22:08
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    Whilst this may technically answer the question, it would be preferable to include the essential parts of the answer here, and provide the link for reference. Blockquotes are an excellent way to do this.
    – Borror0
    Commented Mar 27, 2011 at 20:58
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    The link to the "very good article about the phenomenon" is alas broken. Quite disappointing. Can you correct this ?
    – Evargalo
    Commented Oct 1, 2018 at 15:56
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    @Evargalo: Try this one: lockhaven.edu/~dsimanek/3d/moonillu.htm
    – oosterwal
    Commented Mar 20, 2019 at 13:50

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