The Moon Illusion–Story

Zen and Science (1)

A full moon rises, large and luminous against the horizon. But later at night, when the moon is high in the sky, it has shrunk to a small circle. For centuries, people have tried to explain this observation.

It is easy enough to convince yourself it is an illusion. For example, a photograph taken of a horizon moon will be smaller than that remembered by the observer. The size of the moon in the photograph will remain the same when taken at different heights in the sky. More simply, just compare the size of the moon to the tip of your little finger when held at arm’s length. First, check the moon against your finger when it is first near the horizon, and then check again later when the moon is high in the sky and appears smaller. The relative size measured against the finger remains the same.

There are many theories about the underlying cause of this illusion. An entire technical book, The Mystery of the Moon Illusion, examines these theories. (H.E. Ross & C. Plug, 2002, 275 pgs). The authors conclude that no single theory has emerged victorious. They further observe that The moon illusion is one of the few perceptual phenomena that tap a broad spectrum of sciences: astronomy, optics, physics, physiology, psychology, and philosophy.

Buddhist Comment:

Bodhidharma was a fifth century Buddhist monk credited with bringing Zen from India to China. His surviving writings are few, but to the point:

“Using the mind to look for reality is delusion. Not using the mind to look for reality is awareness.”


Apparently all human beings are wired to make the same perceptual error. The senses may not accurately register what is actually out there. The moon illusion is evaluated against our normal understanding. The assumption is that everyday perception and understanding is accurate. Is that the case? Having seen one inconsistency, there are very likely other illusions, even if we are normally unaware of them. These illusions further distort reality. We may not know what is out there as reality, or even if there is an out there.

Bodhidharma’s comment points in this direction. A mind distorted by illusions from the senses can not explore itself with accuracy. Such an exploration just adds error to error.

In such case, the Buddhist method of examination of reality is through refined awareness, developed by quieting the mind.


Related posts: Feynman Asks a Question

Natural History, Natural Mind


3 Responses to The Moon Illusion–Story

  1. […] in this category: The Moon Illusion; Feynman Asks a […]

  2. Rosemary O'Connell says:


    i want to email this to my nephew: can you add an email send feature to Working with Insight?

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