Summary: Where do rainbows come from? How is rain fall measured? Thousands of volunteers monitor, record, and report rainfall all over the country.

If you’ve ever been walking down a crowded busy street after a mid afternoon rain shower and seen everyone looking up in one direction oohing and ahhing, likely when you looked up you’ve witnessed a rainbow. And no matter how many times you’ve seen one they are nonetheless awe inspiring.

The bands of color arcing across the sunny sky seem to have the ability to make pedestrian traffic come to an almost total halt. Even vehicles will slow down to take a look, parents turning in their seats to point out nature’s magnificence to the wee ones strapped in their car seats. But when your child asks, “Where do rainbows come from?” very few of us have a simple succinct answer offer. Well, to take this load off, I’m going to give you one.

The basis for the formation of a rainbow is refraction, which basically means bending and changing the direction of light. Just like so many other things every day, light moves depending on what kind of path it travels. And, as with so many other things, when something gets in the way of lights’ paths, it may bend – or refract – and because of this it may produce a rainbow. For instance, have you ever been driving in the mid to late afternoon on the highway behind someone who has a crystal hanging from their rear view mirror? No doubt that at points when it shined directly into your eyes you’ve wanted to throw something at them, but what they’re actually doing is lending a perfect example of how rainbows form. When the light hits the multi-faceted crystal just so, it acts as a prism and the light refracts. This splits the light and causes the different wavelengths (colors) of visible light to separate. Longer wavelengths of light (red) are bent the least while shorter wavelengths (violet) are bent the most.

Now in order to see that elusive rainbow in the sky a few things have to take place. First, it has to be raining in one part of the sky and not in the other. Also, the observer of the rainbow has to have the sun behind them. What allows rainbows in the sky to get as huge as they do (and while you’ll never see a monster rainbow coming from a little crystal hanging on a rear view mirror) is that the light is not being refracted by one prism, but millions of little raindrops acting as prisms. Because each color has a different wavelength and bends to a different degree the colors separate create and arc across the sky: a breathtaking rainbow.

Just as it is that there are some places on this planet where it’s dark for six months of every year, or it never snows, or the temperature never drops below 70 degrees, there are many places in the world where it never rains. Some places in the United States like Quillayute, Washington can get over 100 inches of rain a year while Phoenix, Arizona will often not see even an inch in a given month. The Amazonian Rainforest gets over nine feet of rain a year!

But who measures rainfall and how is it measured? Is it just a bunch of people with buckets and rulers?

First of all we have to define what measurable rainfall really is. It isn’t as simple as “the rain that falls from the sky, it’s technically ”the amount of rain that would have remained on the ground if it did not run off or soak in.” Meteorologists and other scientists use various sorts of rain gauges to determine how much rain a given area gets over a period of time.

Rain gauges can be all sorts of things, some of which can add scientific and visual interest to your garden. Others are used by the National Weather Service and other organizations to track rainfall. This doesn’t necessarily mean that they’re overly complicated: according to Wendell Bechtold of the St. Louis Weather Forecast Office the NWS official rain gauge is nothing more than an eight-inch diameter metal tube. Some gauges use radar to garner results, some weigh the rain, and others that are used out in the ocean record the sound of the rain from beneath the water. Many gauges results are recorded digitally or electronically and then sent to computers to be analyzed later. Where the NWS in concerned, they rely on thousands of volunteers to monitor, record, and report rainfall all over the country. Yes, it can be as simple as that.

For those who live in some of the more temperate climates such as Los Angeles, rain is a pleasant change from the day-in day-out, never-changing, 75 degrees and sunniness. For others who see more of it, it can wear a little thin. A friend of mine, and former Seattle resident, once commented on how when you went outside you were never really wet. There was always something heavier than a mist coming down that was very often not enough to warrant an umbrella. Enough, he pointed out though, to make you go crazy. (He also liked to point out the disproportionate number of serial killers and such that sprung from the Pacific Northwest.) Another friend said that a Portland summer was your beautiful reward for putting up with the Oregon weather for the rest of the year.

But to a lot of us the rain comes and goes. It does things we like: waters our gardens and lawns, coaxes nature’s creatures out of hiding, gives kids puddles to jump in.

And if you want to amaze your friends and predict rainfall with total accuracy, there’s only one way:

Wash your car.

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