The Mysterious Rainbow
THE rainbow has long fascinated man, but he has been repeatedly baffled by the mysteries it presents.
Why does the rainbow appear only after certain rains? Why can one see more colors in one rainbow than in another? Why does the bow seem to move away from a person as he walks toward it? Do you know?
Fearing what they could not understand, many ancient peoples viewed the beautiful bow as a hostile force or “bad luck.” To some it was a great snake (or other animal) that swallowed water and held back rain. These views, however, strongly contrast with the first written record of a rainbow.
The First Rainbow
The world’s oldest history book, the Bible, draws attention to the first rainbow and gives the reason for its continued appearance. It reports that God made a covenant, a promise to the survivors of the world flood, namely, Noah and his family, that “no more will the waters become a deluge to bring all flesh to ruin.” And as a sign of this covenant, God said to Noah: “My rainbow I do give in the cloud, and it must serve as a sign of the covenant between me and the earth.” (Gen. 9:8-16) What a splendid way to remind mankind of God’s promise!
Some argue that the Bible was not actually here describing the first appearance of a rainbow, but that from that time forward a new significance was being attached to its existence. However, the Bible presents it as something introduced at that time. Apparently atmospheric conditions prior to the great Flood did not allow for the formation of the rainbow. Even today certain atmospheric conditions must exist for it to appear.
Although the Bible’s comments are brief, they give the why of the rainbow, and to this day those of faith see in it reassurance that God still cares for man.
Attempts to Understand
It was when man began to ponder the how, the mechanics of the rainbow, that he tackled a mystery with many a surprising turn. Truly, those who would “catch the rainbow” have often ended up with sore feet!
One early “detective,” the Greek philosopher Aristotle, held that the rainbow was formed by rays reflecting or bouncing off the uneven surface of cloud droplets. He further reasoned that there were only three colors in the rainbow—a view that dominated scientific thought on the point for centuries. His explanations, however, left many questions unanswered.
One perplexing puzzle arose when two arcs or a “double rainbow” would appear. Why, if the rainbow was simply reflection, would the bands of color in the outer arc appear in exactly the opposite order of those in the inner bow? As various theories on this and other aspects were discarded, scholar Roger Bacon was prompted to say: “It is certain regarding philosophers that no one of them has been able to gain a knowledge of the rainbow.”
‘Not so,’ answered René Descartes, a French scientist of the seventeenth century. Using complex mathematical calculations, he set forth charts showing the angles necessary to the formation of a rainbow. He boasted that those who understood his theories would “easily understand” the cause of rainbows. However, a professor of mathematics at Brooklyn College said that “he had not really answered all the problems connected with the rainbow.” For example, he failed to explain correctly color formation and multiple rainbows.
Then, sixty-seven years later, Isaac Newton published his Opticks, correctly stating that sunlight can be separated into several colors and thus raindrops simply separate the colors. After this, it was generally assumed that “the last word had been written.” But was the mystery of the rainbow really solved? Many thought so. However, the rainbows that occasionally appeared refused to obey the man-made rules.
Eventually scientists began to believe that light consisted of “waves” similar in action to sound waves. Explanation along these lines led the Encyclopædia Britannica for 1858 to conclude: “At last we begin to believe that we understand this matter [the formation of the rainbow] completely.” In fact, so confident were many, that the then-held views on light were commonly called “the complete theory.” However, new experiments eventually reduced the “complete theory” to what was renamed a “first approximation”!
The Present View
Of course, in hundreds of years of studying “clues” scientists have made some fascinating observations about the formation of the mystery bow. Basically, the present view is that you see a rainbow when the sun is behind you and rain is falling in front of you. Remembering that sunlight can actually produce several colors, consider what happens when rays of sunlight hit raindrops at certain angles.
As a ray hits the outer edge of the round raindrop, it is bent (refracted) and dispersed or separated into different colors (different lengths of light waves). Then these separated light waves hit the far side of the raindrop and are turned back (reflected). On their leaving the raindrop, more bending of the waves takes place.
How does this cause all the colors of the rainbow? Well, present theory holds that each color that you see is formed by rays that reach your eye at a certain angle, and the angle for that color never changes. The top band, for example, is red because that portion of the raindrops is at about a 42-degree angle from your eye. It is at that angle that your eye will pick up the red light waves. The other six color bands below the red (orange, yellow, green, blue, indigo and violet) occur at angles slightly less than 42 degrees.
Why, then, when there are two bows, do the colors in the higher one appear in reverse order, with red at the bottom and violet at the top? Because, it is explained, rays of sunlight hitting at an angle of about 51 degrees from your eye are entering the bottom of water droplets and undergoing double internal reflection—in other words, bouncing twice inside the raindrop before coming out of it. This second bounce or reflection causes the colors in the higher bow to be in exactly the opposite order of those in the lower bow.
As for one reason why you can sometimes see more colors than at other times, the February 1972 Science Digest notes: “The number of colors and their relative widths in the rainbow vary with the size of the raindrops.” But there is yet another factor—you. Since the rainbow is only visible when you form a certain angle with the raindrops, it really could be called your rainbow—your personal “seeing experience.” So the same raindrop that is at an angle to reflect red light to you may be reflecting yellow or blue light toward another person standing a few feet to one side of you.
Of course, this means that when you move, the rainbow “moves” also. That is, if you walk toward a rainbow, you may pass the position of the raindrops that formed the first rainbow you saw, but you will not be able to look up and see a rainbow over your head, for you are at the wrong angle. You may still see a rainbow in the distance, but this will be a new one formed at the appropriate angle from your new position. How accurate the old saying that describes the foolish dreamer as “chasing rainbows”!
Thus we can see that man has gradually learned much about the great bow of light. But does this mean that the final chapters to this mystery story have been written?
The Mystery Remains
“After hundreds of years of study, what is left to answer?” was a common attitude early in our century. According to many, the “light and optical theory seemed complete and perfect.” But, again, questions persisted, this time concerning the very basis of the rainbow—light. Experiments indicated that light rays sometimes acted like particles (small pieces of matter) instead of “waves.” This upset the “wave theory,” which had been apparently successful in explaining so many different activities of light.
More research has led to yet another theory in which light is now viewed as composed of particles called photons and yet in action behaving “wavelike and particlelike at the same time.” In the final analysis, we must humbly admit that man still cannot fully answer the question that God asked Job over 3,000 years ago: “Where, now, is the way by which the light distributes itself?”—Job 38:24.
But the very nature of light is not the only remaining puzzle in the rainbow mystery. “Little has been learned about its perception,” says the book The Rainbow. Yes, there is still much to be learned about the human eye and especially concerning color vision.
Truly, the challenge of the rainbow remains. And so whether we view the ‘bow of heaven’ as a sign of peace or choose to study the mystery of its structure, we do well to stand in awe of its Designer. It is true in many ways that no one is about to catch the elusive rainbow!
[Diagram on page 15]
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