Despite the fact that the rainbow looks like a real object hanging somewhere in the distance, all attempts to approach it will be doomed to failure – it will move away from us at the same speed with which we approach it. It won't be possible to catch it either – after all, a rainbow is an optical object that does not exist at a certain point in space. In fact, a rainbow is a wonderful illusion, by understanding the nature of which you can learn a lot about the world around you and the Universe. Thus, ancient civilizations had much more difficulty understanding the nature of light than with physical objects and even considered it as a mechanism of vision, leading to the appearance of such oddities as rainbows. The ancient Greeks, for example, were sure that everything around them consists of four elements, so the seven colors of the rainbow were perceived by them as a manifestation of divine will.
What is the real magic of the rainbow? Image: images.newscientist.com
Contents
- 1 The Mystery of Light
- 2 The Light Spectrum
- 3 Newton's experiments
- 4 Why do we see rainbows?
The mystery of light
Isaac Newton is rightly considered one of the greatest scientists in human history. And it’s not just the theory of gravity, which he developed in the seventeenth century and which describes the movement of objects near the Earth’s surface, the orbit of the Moon around the Earth and the orbits of planets around the Sun. It was Newton who discovered that white light is a mixture of all colors.
The scientist came to this conclusion after conducting an experiment. First, he darkened his room in such a way that not a single ray of light could penetrate it. Then he parted the curtains so that a ray of light, as thick as a pencil, broke through and passed through a prism – a triangular piece of glass.
White light is a mixture of all colors. Image: cdn.britannica.com
The prism, as it turned out, refracted a narrow beam of white light in such a way that when it came out of it, it ceased to be white, becoming multi-colored, just like a rainbow. Newton called his artificial rainbow a spectrum.
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Light spectrum
The spectrum that Newton spoke about is arranged as follows – when a ray of light passes through the air and hits into glass, it is refracted. Note that refraction is called refraction, which, in turn, occurs not only in glass, but also in water. This is especially important to remember when we talk about rainbows, because it is due to refraction that the oar appears curved when we plunge it into the river.
So, light is refracted when it passes through glass or water, but the main thing in this process is the angle of refraction, which directly depends on the color of the light beam. Thus, red light is refracted at a more obtuse angle than blue light.
Newton was right when he suggested that white light is a mixture of different colors. Image: www.mozaweb.com
Thus, if we pass white light through a prism, we will see that blue light will refract more than red light, so when they come out the other side of the prism, they will separate, and between them there will be yellow and green. As a result, we will see a Newtonian spectrum: all the colors of the rainbow, arranged in the usual order for a rainbow – red, orange, green, blue, indigo, violet.
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Newton's Experiments
Of course, Isaac Newton was not the first person to create a rainbow using a prism – other experimenters got the same result, but they believed that it was a prism « colors» White light. Newton looked at the rainbow differently and suggested that the prism simply separates the colors from each other.
Newton later proved the validity of his guess with a series of experiments. He took a prism, as before, and directed a multi-colored stream of light into a small slit, so that only one color, for example, red, passed through it. Then he installed another prism in the path of the red beam, which refracted the light as usual, but at the exit the beam remained red – no additional colors appeared.
Newton solved the mystery of light and the rainbow. Image: www.thoughtco.com
Thus, the outstanding scientist confirmed his theory about white light as a mixture of all colors and… continued experiments. So, the next time Newton decided to become more inventive and used three prisms at once. In fact, it was a control experiment that finally resolved the scientific dispute of those years.
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Why do we see a rainbow ?
So, we've got the prisms figured out, but what about a real rainbow? To understand how it is formed, it is necessary to remember about refraction, since a rainbow appears when sunlight reflects from raindrops and enters the eyes of the observer. Most raindrops are spherical, which provides the conditions necessary for a rainbow to appear.
To see a rainbow, other conditions are necessary, including the position of the sun and raindrops in relation to the observer. This means that the sun should be behind us, low above the horizon (ideally at an angle of at least 42°). The lower the sun goes in the sky, the larger the arc of the rainbow we will see. A rainbow appears semicircular over a flat surface only at sunrise or sunset, when the sun is exactly above the horizon. In most cases, a smaller portion of the arc is visible.
A number of important conditions are necessary for a rainbow to form. Image: images.ctfassets.net
Rain, fog or any other source of formation of water drops should also be in our field of vision, but the size of the rain drops directly does not affect the geometry of the rainbow, but fog or haze tends to enhance the effect.
Note that sunlight consists of light with many different wavelengths that are slowed down by different amounts, causing the white light to split or scatter. In this case, the shorter blue and violet wavelengths change direction slightly towards the longer wavelengths of red light. Because water is denser than air, light passing from air into a raindrop at a certain angle slows down and changes direction in a process called refraction.
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p>Thus, the observer, being in the right place, will see how the scattered sunlight is reflected back towards him. Light scattered by many droplets will appear as a multi-colored rainbow when entering the observer's eye.
Different colors emerge from the droplets at angles varying by about two degrees, from red to violet. The red light seen by the observer comes from droplets that are located slightly higher in the atmosphere than those that scatter violet light in the direction of the observer.
A rainbow is a beautiful illusion that hides the nature of light. Image: timesknowledge.wwmindia.com
The human eye can distinguish many shades, so it is generally accepted that the rainbow consists of seven colors: red, orange, yellow, green, blue, indigo and violet. So it's time to remember the famous children's counting rhyme that denotes the seven colors of the rainbow – “Every hunter wants to know where the pheasant sits.”