Weather Whys; Orange Moon

This is weather-wise. Some nights, the full moon rises huge and orange above the horizon, or at least it seems that way. Actually, the moon is its normal size and color, but it looks different because the light from the moon is scattered and bent as it passes through the atmosphere. In fact, the same effect that makes for beautiful red sunsets causes the big orange moon. When the sun is low in the sky, it's rays pass through a lot of atmosphere to reach our eyes, a lot more, in fact, than when it's at a higher angle. And the lower atmosphere is often full of pollution particles, dust and smoke from both man-made and natural sources. That screen of dust and smoke acts kind of like a sieve for incoming white light, which is actually made up of a rainbow of colors. When light from the sun passes through all that dust and smoke, the blue, violet, and green shades don't make it through. They get scattered, so only the orange, yellow, and red colors make it to your eyes. Now, it works the same way for the moon.

Of course, the light coming from the moon is really just reflected sunlight, but it gets scattered just the same when it goes through a lot of atmosphere. So when the moon is low on the horizon, it too often looks orange. But what about the size? Well, believe it or not, if you objectively measure the apparent diameter of the moon, you'll find it's the same size no matter where it is in the sky. Your brain tells you the lower moon looks larger because there are things on the horizon to compare it with, like houses and trees, but when it moves higher, it looks small against the backdrop of the vast sky. For instructions on how to measure the moon, write to moon size, care of KGOU radio, Norman Oklahoma 73019. Otherwise is made possible by a grant from the National Science Foundation. Our writer is Christine Harbor, our editor, Brian Walking, and our executive producer, Karen Hope. And for weather wise, I'm Drew Barlow.