Why Isn’t “The Moon Illusion” a Lot More Famous Than it Seems to Be?
I’ve been a fan of the “Great Courses” (renamed “Wondrium”) for some time now. Recently, I began one on the entire history of Psychology, complete with entire lectures on how each individual sense organ works (in order to explain “perception”, etc). Yes, it’s quite thorough, and the professor is apparently some legendary Oxford Don, because the course was filmed for the series back in the 1990’s, and they’re still offering it.
At one point, the professor gives an example of an illusion of “perception” which has baffled Mankind for thousands of years, and even Nasa admits that it has never not been completely explained (“Why do we see the Moon Illusion? Brace yourself- we don’t really know.”).
I’ve been rather preoccupied by it ever since. I’m not sure there is such a “in-your-face”, unexplained, phenomenon of Nature to quite match it.
And yes: it’s cleverly called “The Moon Illusion”.
And this is why:
Go out any night and look at the moon on the horizon when it first is visible. It generally is pretty big. Then, go out and look a few hours later, when the moon is much further up in the sky. You maybe surprised to note that it actually seems just a fraction of the size that it appeared when it was close to the horizon. Yet, in reality, if one was to measure the two moons, they are exactly the same size (the horizon moon, in fact, is the one which is slightly smaller ((1.5%)) because, at the time, it is 4000 more miles away from the earth.)
This really is quite astonishing, if one sits and ponders it.
It’s also remarkable how many very well-educated people whom one mentions this to, are completely unfamiliar with it. I know I hadn’t heard about it until now, when well into my 60s.
Go out some evening, and take a look…
Further reading: Moon Illusion: Why Does the Full Moon Look Bigger on the Horizon?
