Good day, dear Take in Mind readers!
Please raise your hand if you did not memorize the magic name “Roy G. Biv” in your childhood? Or, in its advanced form: “Richard Of York Gave Battle In Vain”?
No doubt, a rainbow is one of the most beautiful and beloved miracles of Nature. Just imagine: the sky is getting dark, clouds above you, then, a bright flash of lightning illuminates the sky with a dazzling white light, then thunder, and finally rain… Eventually, the rain ends, and the sun comes out, finally visible through the clouds, illuminating the refreshed nature. All around is filled with the smell of ozone. And then its majesty The Rainbow appears. The rainbow, a colorful atmospheric phantom created by sunlight and raindrops, appears for a short time and melts without a trace. What words can describe this? Only one word comes to mind: magic! Probably, this is the reason why today as well as thousands of years ago a rainbow causes a truly childish delight for all the people. Just as an experiment, go outside after the rain and see how many adults admire this gift of nature with half-open mouths and smiles.
Formed by the suspension of invisible raindrops, a rainbow appears and disappears as if by magic. Maybe that is why in ancient religions and traditions in different parts of Earth it is believed that higher forces are involved in the appearance of the rainbow.
In Scandinavian mythology, a rainbow is the Bifrost Bridge connecting the people’s world, Midgard, and the world of gods, Asgard. The ancient Chinese goddess of lightning, Tien Mu, wore a multi-color rainbow mantle. The Mayan goddess Ah-Chel, the mother of the people, was also known as The Rainbow Lady. The Mordvin-Moksha god At’am and the Sami god Tirmes are armed with a bow, i.e., with a rainbow. Bantu people called the rainbow as the bow of Lesa, the supreme god of many African tribes. According to the traditions of the Australian aborigines, the rainbow serpent, a modern world foremother, symbolizes the transforming force acting in nature and human society, and so on and so forth.
And now a little bit about optics and biology. How is a rainbow formed and why do we see the whole color spectrum in it? An excellent description of the whole process was given by the American astronomer Dr. Edwin G. Krapp in his book “Beyond the Blue Horizon. Myths and Legends of the Sun, Moon, Stars, and Planets”. Here we present a short summary of his article. A rainbow is formed by the passage of sunlight through raindrops. Each drop can be presented as a spherical glass aquarium. Light enters into the raindrops from one end, then it is reflected from the inner surface and exits from the other end. Inside the drop, the sun’s beam bends slightly, because the refractive index of water is higher than that of air. The speed of light decreases slightly when it passes from air to water, and again increases when it goes into the atmosphere. Different colors of the spectrum are refracted at different angles since their speed decreases not quite proportionally. The violet color is refracted to the greatest, and red – to the least extent, and the white sunlight is actually a combination of all the colors.
Each one sees his or her personal rainbow. Moreover, each eye sees the rainbow in its own way. For us to able to see a rainbow, the light must pass the way from the raindrop, which refracts it and decomposes into composite colors, to the pupil of our eye. Raindrops sending light into the eyes of one person cannot direct it into the eyes of another person. This is a “task” of other drops and each of them creates different rainbows.
Since the sky, to some extent, creates a rainbow from mirrors (the drops), the sun is always in the opposite direction of the rainbow. A rainbow is only a part of a circle, and the size of the visible segment depends on the height of the sun above the horizon. When the sun is high, the rainbow is low and shallow, when the Sun is closer to the horizon, the rainbow is high and steep. However, looking from the surface of the earth, we cannot see more than half of the circle. This changes when we look from top to bottom from a great height – for example, in a low valley from the top of a mountain. Where the earth begins, raindrops end. But, for example, when you are near the plane’s window, and if the sun is above your head and raindrops are below, you can see the full rainbow’s circle.
We see the arc form because the raindrops basically have the same shape and refract most of the light at an angle of 42 degrees. With such an angle between the sun and the eye, any drop of rain can send all the colors to our retina. This means that the droplets are located at an angular radius of 42 degrees from the place that seems to us as the rainbow’s center. If they are all at the same distance from the observation point, then they would form a complete circle.
In addition to the wonderful description of Dr. Krapp, we want to add a small comment regarding the formation of another, so-called secondary, rainbow. This less bright rainbow (appearing around the primary) is formed by sunlight that is reflected twice in the drops. In the secondary rainbow, there is an angular radius of 50–53 degrees from the center that is seen by us. Another interesting difference from the primary rainbow is the “inverted” order of colors (violet is above and red is below).
Actually, we can finish this post here. The physical background is clear and there seems to be no magic at all. But next time, when a rainbow appears in the sky, hundreds of children and adults cannot ignore this wonderful sight. Therefore, we cannot deny ourselves the joy of quoting Neil Gaiman’s “Odd and the Frost Giants”:
“I think the rainbows are imprisoned in the ice when the water freezes… And I thought, Ice is only water, so it must have rainbows in it too. When the water freezes, the rainbows are trapped in it, like fish in a shallow pool. And the sunlight sets them free…”
P.S. When we wrote this post, we searched for the mnemonic devices that help to remember the order of the rainbow’s colors. Here are a couple of examples that the internet has suggested:
- Read Out Your Good Book In Verse
- Richard Of York Got Buggered In Venice
So, dear readers, we offer a mini-competition for a new magic formula for remembering the rainbow colors. Please write your suggestion in the comments.
Featured image – a rainbow. Own work.
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