A rainbow is a semi-circular color spectrum appearing in the sky due to the result of refraction and multiple reflections of sunlight in droplets of water. Rainbows appear when water droplets are lit by direct sunlight, a condition that rarely occurs during a storm, because the clouds block the sun. Rainbows are frequently seen after a storm, when the falling rain has moved into the distance and the sun is roughly behind the observer when the observer is facing the patch of rain.
According to Genesis 9:11-17, after the Flood God told Noah that henceforth the rainbow would remind God and Mankind of God's promise never to flood the Earth again. Physics can explain the appearance of rainbows accurately as the result of refraction and multiple reflections of sunlight in droplets of water, but not the feelings of awe and spirituality rainbows inspire, as they did in William Wordsworth when he wrote:
My heart leaps up when I behold
A rainbow in the sky:
So was it when my life began;
So is it now I am a man;
So be it when I shall grow old,
Or let me die!
The Child is father of the Man;
I could wish my days to be
Bound each to each by natural piety.
Complete circular rainbows can be seen under the right conditions; in particular, when viewing the mists over Niagara Falls early or late in the day. Circular rainbows can sometimes be seen from an airplane when it flies over clouds, the rainbow actually encircling the airplane's shadow on the clouds. One way to think about the rainbow is that the mist or rain is like a projection screen, and the rainbow can only be seen where the projection screen is. When the projection screen is large enough, you see the entire circular rainbow.
The rainbow is often depicted inaccurately in pictures. For example, it may be depicted as a three-dimensional object, with perspective, real rainbows never have this appearance. Real rainbows show an extremely subtle blending of color. It is hard to pick out separate colors in a rainbow, but of course to the extent that one can, they appear in the "Roy G. Biv" order, red outermost, then orange, yellow, green, and a range of bluish shades which, in a real rainbow, are hard to distinguish and name.
It is extremely difficult to reproduce the subtle, faint pastel colors of a rainbow on a printed page, or even in a color photograph, partly because a rainbow contains colors that are not within the gamut that can be produced by mixing three primaries, and partly because rainbows are faint; printed depictions of them almost invariably have been enhanced to make them look brighter and more intensely colored than they really are.
- Genesis 9:11-17, "And it shall come to pass, when I bring a cloud over the earth, that the bow shall be seen in the cloud: And I will remember my covenant, which is between me and you and every living creature of all flesh; and the waters shall no more become a flood to destroy all flesh."
- William Wordsworth, "My Heart Leaps Up When I Behold (1802)
- Leprechaun A typical, but utterly unrealistic depiction of a rainbow. This picture also shows the rainbow as if it had separated, sharp-edged bands of color, in the order yellow, orange, red, green, blue.