The moon illusion and human delusion

I am sure most of us have marveled at the beautiful, larger-than-usual moon at the horizon on a full moon night. In addition to being a beautiful sight, the full moon on the horizon can also teach us something very profound about the human mind and also about the nature of truth.

Before proceeding any further, I want to mention a quick fact. In case you do not agree with this, please try this for yourself on the next full moon day before reading beyond this paragraph. On a full moon night, after seeing the moon on the horizon, if you see the moon again after it has moved up in the sky, you will notice that its size is obviously smaller than before.

The key question is this -- why? Why did the size of the moon change in a matter of couple of hours?

When this question is put to people (believe me, I have asked dozens of my friends and acquaintances), the most common answer is that the moon is closer to the earth in the evening। This is a very logical answer -- you can obviously see a change in size of the moon. You vaguely remember something about the elliptical orbits of planets and moons. You may even remember about the perigee and apogee of the ellipse that you studied long time back! So this is the natural answer that comes to your mind॥ what could possibly be wrong with this answer? (There are other similar plausible stories like thinner atmosphere etc. All such stories will have 'scientific sounding' explanations.)

Now, imagine people's fury when I tell them that the apparent change in the size of the moon is an optical illusion. I get some very predictable responses. First and foremost, I get some very strange stares! Then come words like 'bullshit' or 'nonsense'. Even if people do not say these words out loud, they are convinced that you are bullshitting and you can see it in their eyes. Very very few people actually ask the correct next questions -- why/how is that?

I hope you, the reader, is one of those very few who ask the right questions ;) .. And here is the simple experiment you can do to prove this to yourself. Take a small coin (eg. 25 paisa or 5 cent). On a full moon night, when you see that the moon is big, find out the distance you have to keep the coin from your face to exactly block out the moon completely. Remember this distance. Now, repeat the experiment when the moon looks smaller on the same night. Make sure you repeat the measurement process several times on both occasions to get accurate results. Compare the two numbers. You will see that they match 100%, proving that the real size of the moon has not changed at all.

If you want more details, please start here:

• http://en.wikipedia.org/wiki/Moon_illusion
• http://science.nasa.gov/science-news/science-at-nasa/2005/20jun_moonillusion/
  

So, here are the 'profound' lessons I promised earlier ;)

• Truth, even in hard sciences, is often hidden in plain view but it can still be subtle
  
• Denial is often our first response when our world view is challenged. This should not be the case if we are really going to learn from each other
  
• Human brain and the sense organs play many tricks on us. We can suffer from mass delusions. This is not only a Vedantic claim, but also hard science.
  

Notes and disclaimers:

• There is no dispute that moon illusion is an optical illusion. But the precise explanation for that is still controversial. You can google and find out more if you are interested ;)
• The reason I blogged about this first is that I find that the 'denial response' is the biggest block for people to really learn anything worthwhile. So by making people (myself included) aware of this, I hope that their natural inhibitions will reduce.