THE JOY AND SCIENCE OF RAINBOWS

January 05, 2008 12:00 am

By Scott Graves

Pilot staff writer

It's rainbow season.

The time of year when rain showers and sunshine often mix, resulting in stunning, yet fleeting rainbows in our sky.

My family spotted four within a half-hour period during a recent drive through the rain-drenched mountains. We drove right past the end of one of those rainbows as it fell to the side of the highway.

"Where's the pot of gold?" my 4-year-old daughter said.

"I think the leprechauns already grabbed it and hid it in the trees there. They don't like to share," I offered.

I don't think she bought it.

We continued to look for more rainbows, spotting two more before the clouds shut the sun out completely.

When I asked Alia what makes a rainbow, she replied, "It's when the sunshine hits the raindrops and turns them into sparkling jewels."

Well, she got it half right, but I left it at that because, to be honest, I couldn't recall the exact scientific explanation of a rainbow – at least enough to explain it in plain English. Hence the incentive to look it up, and a good topic for a column.

Webster's Dictionary describes a rainbow as "an arc or circle that exhibits in concentric bands the colors of the spectrum and that is formed opposite the sun by the refraction and reflection of the sun's rays in raindrops, spray or mist."

Huh?

I searched the Internet extensively for information. (I get paid to do this!) I distilled the many explanations I found into a simple version:

Sunlight is made up of many colors, but you can't normally see them – the sunlight just looks white or yellow. A rainbow is caused by sunlight hitting raindrops in a certain way that breaks the light up into all the colors that are normally jumbled together.

I learned more than I bargained for during my research about rainbows. For example, did you know that a rainbow is actually a circle? They can be seen when we look down from planes flying high above the earth. Standing on the ground, we can only see half of the circle because the lower part is cut off by the earth.

Which begs another explanation: According to my research, a rainbow does not actually exist at a particular location in the sky. It is an optical illusion whose apparent position depends on the observer's location and the position of the sun.

The time when people are likely to see a complete rainbow is when looking up at the winter night sky. That ring around the moon, also known as a moonbow, is caused by the refraction of moonlight (which of course is reflected sunlight) on ice crystals in the earth's upper atmosphere. The moonbow is white because the weak sunlight does not contain enough color for the human eye to see.

I could cite more jargon about the science of rainbows and moonbows, but it just makes my head spin.

Suffice it to say that rainbows are cool, beautiful phenomenas of nature. To my daughter, they are simply magic, and she's right.

Now, if only we can keep those darn leprechauns from hiding that pot of gold.