|
|
|
|
Moonbows
Mon Jul 28, 2003
Listen in RealAudio 
Although not as spectacular as solar rainbows, the rare lunar rainbow or "moonbow" is as
thrilling for the weather watcher as a birder spotting a Strix nebulosa. Hi, I'm Bryan Yeaton
for The Weather Notebook. That's a Great Grey Owl, by the way.
Moonbows form the same 42-degree arc as rainbows, but to the naked eye, they appear a delicate
white, or even black, rather than multi-hued. They've been described as eerie and ghost-like,
like moonlight that spawns them.
They form just as daylight rainbows do. When the moonlight strikes drops of falling rain in
the sky opposite the moon, it is reflected and refracted within the raindrop, which acts like
a prism and separates the moonlight into the rainbow spectrum.
Because moonlight is reflected sunlight, it has the same colour spectrum as sunlight. But we
see the moonbow as essentially colourless because our eyes don't perceive colours well in
low-light. A camera, however, can catch the colours and produce a photo which looks just like
a rainbow.
Since the moonlight is weaker than sunlight, about the only time you can see a moonbow is when
the moon is full or nearly full. And, you also need rain to make a moonbow. Because they are
so faint, moonbows are easily obscured by light and air pollution present around most cities.
For these reasons and since scattered showers are more common during the day moonbows are a
rare sight, indeed.
Two locations noted for their frequent moonbow observations are Kentucky's Cumberland Falls
and Africa's Victoria Falls. There, the bows form from drops in the waterfall mist.
Reportedly, Niagara Falls once had frequent moonbows, but they are now overwhelmed by the
surrounding lights.
Thanks to our contributing writer, meteorologist Keith Heidorn. Our show is produced by the
Mount Washington Observatory, with funding from Subaru, and the National Science Foundation.
Today's Links
Moon Light Effects
http://home.hiwaay.net/~krcool/Astro/moon/moonring/
|
|
