The rainbow. Our covenant

Christians from the earliest times have well understood the significance of a rainbow and, to this day, unquestioning believers can readily exchange knowing glances to counter the perplexity forged on the faces of the doubters.

Indeed the Bible sets out for all to know, in the Book of Genesis, that when the earth had dried, following the Great Flood, God made his covenant with Noah to nevermore use water to waste the land. In chapter nine, verses 1215, we read: And God said to Noah. “Here is the sign of the covenant I make between myself and you and every living creature with you for all generations. I set my bow in the clouds and it shall be a sign of the covenant between me and the earth. When I gather the clouds over the earth and the bow appears in the clouds, I will recall the covenant between myself and you, and every living creature of any kind. And so the waters shall never again become a flood to destroy all things of flesh.”

To the faithful then, the rainbow is indeed the mysterious arc in the sky described in this biblical covenant, and there has always been those amongst their ranks most hesitant to delve too deeply into such things, almost seeing that kind of interest as an impertinence. However, man being man, mysteries are there to be probed until they are solved and, certainly towards this end, many interesting facts have emerged concerning the nature and appearance of the rainbow.

Most people would seem vaguely to appreciate that a rainbow is formed when rays of light from the sun are somehow reflected and dispersed by raindrops. This of course is basically what occurs, but fewer people are aware that certain very precise atmospheric conditions must prevail before a rainbow can appear.

A bow can only occur when there is a clear strong sun, no more than 42 degrees above the horizon on one side, (be it east or west), and passing rain clouds on the other. Thus the most impressive arcs are seen quite early or late in the day, and when the sun is directly behind the observer. In consequence it is clear that, in the morning, a rainbow can only appear in the western sky while, conversely, during the late afternoon or evening, it must be seen in the east.

To witness a colour-intense rainbow is an extremely personal experience. It is truly ‘your rainbow’ since its occurrence is directly related to the position of the observer. Nobody else, however close they might be, will be able to see quite the same bow, for no two people’s eyes can be in the same place at the same time. When the observer moves, the rainbow moves too for, though it lies in a precise direction with regard to the viewer, it has no definite position. If the observer approaches the rainbow it will recede. If he departs it will follow.

A rainbow’s hues are the simple colours of the solar spectrum, with the sequence from the inside commencing with violet passing through indigo, blue, green, yellow, orange to the outer red. The order of colours in this, the major or primary bow, never changes, though the width of the individual colour bands can vary considerably from bow to bow. With a double rainbow the colours are the same in the secondary and fainter arc though, oddly, they are in reverse order, with red as the inner colour of the arc.

The view remains common, by no means amongst children only, that a rainbow is just a semi-circle with its ends firmly rooted in the earth’s surface. Many find it hard to accept that it is indeed a full circle suspended in space, with the other half hidden from our gaze be the curvature of the earth. Though, from a flat low-lying surface, half the rain circle is all that is likely to be seen, the area of the visible bow increases the higher the altitude of the observer. Under favourable conditions, from a high mountain or in an aeroplane, the complete rain circle can sometimes be seen. So striking is the full circle that witnesses are said never to forget the experience.

Sometimes people are puzzled as to why rainbows fail to appear towards the middle of the day when the sun is more directly overhead, even though all other atmospheric conditions would seem to be favourable. Since it is a projected line from the sun passing through the viewer’s eye to the ground ahead which marks the centre of the rain circle and enables the upper half to be seen in the sky, it will be clear when the sun is almost directly overhead, (with therefore the projected line through the eye striking the ground right at the observers feet), that there is no scope for any part of the circle to appear.

Those aspects of the rainbow’s nature which science has so far managed to probe may go some way towards prising out its numerous secrets but, for every question answered there are many as yet unexplained. Great mind will no doubt continue to puzzle over the still largely inexplicable way in which rays of sunlight bombard a shower of raindrops. May the pure magic of the process long thwart such endeavours.

In full accord with the continuing fight-back of Genesis as claimant to being the true storehouse of galactic wisdom, the creationists are content to leave aside the restless attempt to pin down the supernatural by accepting the rainbow for what it is a glorious emanation in the heavens beyond mere mortal comprehension. (Antony Hebdon)

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