Post by Chicago Astronomer - Astro Joe on Jun 26, 2005 12:31:06 GMT -6
Why does the moon look so big now?
From the BBC...
Last Updated: Friday, 24 June, 2005, 12:45 GMT 13:45 UK
Why does the moon look so big now?
For the past few nights the moon has appeared larger than many people have seen it for almost 20 years. It is the world's largest optical illusion, and one of its most enduring mysteries.
It can put a man in space, land a probe on Mars, but Nasa can't explain why the moon appears bigger when it's on the horizon than when it's high in the night sky.
The mystery of the Moon Illusion, witnessed by millions of people this week, has puzzled great thinkers for centuries. There have even been books devoted to the matter.
Not since June 1987 has the moon been this low in the sky, accentuating the illusion even further. But opinion differs on why there is such an apparent discrepancy in size between a moon on the horizon and one in the distant sky.
The theory runs that we believe things immediately overhead, flying birds for example, are closer than birds on the horizon. When the moon is on the horizon, the brain therefore miscalculates its true size and distance.
Then there are those who scoff that this is an illusion at all. They, at least, can be proved wrong. Hold a coin up to a low-lying moon to and compare differences in size. Any difference will remain exactly the same, as one traces the trajectory of the moon through the night.
Indeed, it's said that by viewing a low moon though a rolled up piece of paper, to block out the surroundings, the illusion immediately vanishes.
But experts have yet to agree on either or, indeed, any explanation. For the moment at least, the real reason for the Moon Illusion remains up in the air.
More here: news.bbc.co.uk/2/hi/uk_news/magazine/4619063.stm
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I think I'll try the rolled up paper experiment to see for myself.