Thursday, July 29, 2010

Deception of the Eyes- Changing Moon

The most impressive nature’s optical illusions must be the ‘rising moon. When the earth’s satellite appears on the horizon, it sometimes appears to be enormous. This is surprising because the distance from the earth to the moon is more or less fixed. When the moon rises higher, it then appears to shrink to the size we know. How can we explain this? There are several reasons; we, our eyes orientate ourselves according to the horizon, using it as a reference point to estimate distance.  The further the distance to the horizon, the larger the moon will appear. If you hold up your hand, for example, and block off the horizon, you will see the celestial body the same size as it usually appears to be in the sky.

Many experts like to explain this strange phenomenon as follows: in our eyes, the moon is always the same size, whether it low on the horizon or high in the sky. The size of the object is determined when the signals from the sensory organs reach the brain’s visual center; a decisive factor is how we estimate the distance of the moon. When it is near the horizon, we can see trees, houses and other objects which give us an indication as to its distance. It appears to be near at any rate, the brain can estimate its distance, and however, this is nearly impossible when it comes to the vastness of the starry sky.
When the moon rises, we have the impression that it is right on the horizon, at the same distance. This gives us the impression that the earth’s satellite is relatively near and we perceive it as bring much larger.
Other factors probably also play a role in this illusion- for example, the red color of the evening moon or the haze on the horizon. We should enjoy the fact that our brains treat us to such spectacular images- even if they are only illusion. Now, Do you agree the changing moon is the deception of eye?!


  1. Human eye has got its own draw backs; but this one comes much to our own advantage for it enables us to enjoy the beauty of the silver moon in night skies!!!


  2. Interesting thoughts, and cool pics.

    I wonder why the Sun doesn't seem so big while rising.

  3. The horizon-relativity is interesting. I'll definitely try it out soon.


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