Week of November 26-December 2, 2017
Few things in nature are more stunning to watch than an immense orange full moon rising over the horizon. While this occurs every month, on Saturday, Dec. 2., it should be extra-special. Watch this amazing sight just once, however, and you'll surely ask the same question as every other moon gazer: "Why does the moon appear so large and red when it's rising?"
A simple question. Unfortunately, the answer is not so simple.
First off, the moon's orange color originates from the atmosphere around us. The dust-filled air scatters out the bluish light from the moon's spectrum and leaves only warmer colors like yellow, orange and red to shine through. The more particulate matter in the air (such as dust, smog or volcanic ash), the redder the moon will appear.
The seemingly immense size of the rising moon, however, is another matter altogether. Many believe the atmosphere acts like a lens and magnifies the moon's appearance, but this is just as wrong now as it was when Ptolemy suggested it 20 centuries ago.
This striking phenomenon is known as the "moon illusion." It is not created by the moon or atmosphere. Rather, it occurs when our brains are fooled by the terrain behind which the moon appears.
To prove this to yourself, make a loose fist; hold it up to your eye; and look at the rising (large) moon through it, using your fist to block out all but the moon itself. The moon will appear to shrink. For an even more startling demonstration, blink your eyes back and forth, looking through and then around your loose fist, and watch as the moon grows and shrinks. I think you'll agree that it's quite a powerful illusion.
But on Saturday, there's something else going on as well. Not only will the moon illusion be in play; the moon will actually be larger as well.
Wait a minute. How can this be? The moon is a solid hunk of rock; its actual size can't change. True, but its apparent size can change. This effect occurs because the moon doesn't orbit the Earth along a circular path; instead, it moves along an ellipse. At times, it carries the moon either closer to us or farther from us during its monthly cycle. And this weekend, the full moon will be at its closest "perigee" of 2017. Therefore, it will appear larger than normal.
How much larger, you ask? Well, despite the media's insistence on calling this a "supermoon," its relative nearness accounts for only a 7 percent increase in its apparent size, hardly enough for most casual observers to notice without knowing it in advance.
Combine these two effects, however, and you'll have one terrific view on Saturday. To see it at its best, keep in mind that the full moon rises around the same time — and in the opposite direction — as the sun sets. That means that on Dec. 2, you can look for the rising full moon to appear over the east-southeastern landscape during dusk.
If you have a low horizon and a clear sky, you'll definitely be impressed!
Visit Dennis Mammana at www.dennismammana.com. To read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.
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