The secret of the rainbow

  In the evening, after a downpour, the sky cleared, and a rainbow hung over the sky, gorgeous and mysterious. As early as thousands of years ago, the ancients noticed this beautiful natural wonder. In their eyes, the rainbow is a miracle, and they incorporate the rainbow into the myth.
  In Norse mythology, the rainbow is a bridge between the gods and the human world. It is guarded by the god of light, Hemdahl. In ancient Chinese mythology, the rainbow is the radiance of the sacred stone used by the niece. In the Indian mythology, the rainbow is the god of thunder and lightning. The bow of Shi Tiantian; in the Bible, the rainbow is the sign that God and Noah agreed not to flood the world.
  Today, we know that the curved, colorful rainbow is just the result of the collision of light and small water droplets in the air. But how do sunlight and water droplets form a rainbow? The earliest scientific explanation of the rainbow was the ancient Greek philosopher Aristotle.
  The rainbow is an arc of
  300 BC, Aristotle can not help thinking of looking at the rainbow, why are the rainbow arch-like shape. He believes that there is a mirror on the cloud consisting of many small water droplets, which reflect the sunlight and form a rainbow. The angle of reflection of sunlight after a small bead is not arbitrary. Since the sun’s rays are parallel, in small droplets, they will be reflected at the same angle. If you stand between the sun and these small water droplets, face the sun, face the water droplets, and some of the light reflected by the water droplets can just enter your eyes, then in your opinion, the sky where the water droplets are located will be slightly brighter than other places. These slightly brighter places are the rainbows you see. Aristotle is a geologist who discovered that the light reflected by the water droplets is directed in all directions, but the water droplets entering your eyes reflect the light at a fixed angle, with your eyes as the apex, reflecting all the water droplets into the eye. When the light gathers, a cone is formed, and the bottom of the cone is a rainbow.
  So why is the rainbow we see not a whole circle but a partial arc? Aristotle discovered that the position of the rainbow is related to the observer’s eyes and the position of the sun. The center of the circle at the bottom of the cone is the projection of the apex on the underside, and this is just on the extension of the line connecting the sun to your eyes. This means that the higher the sun, the lower the center of the circle, the larger the rainbow is hidden below the horizon, which is why the rainbow we usually see is curved because it is only part of the rainbow. When the sun rises or the sun rises, the sun is almost horizontal and the center moves upwards. At this time, we can see most of the rainbow. At noon, the sun is almost at the top of your head, and the center is almost at your feet, so you can’t see it at noon. rainbow. If you want to see the whole rainbow, sit on the plane and fly high enough or stand on a high mountain top, maybe you have a chance to see it.
  In addition, it is said that there is gold buried under the rainbow. If you walk towards the rainbow and want to dig out the gold, you may have spent all your life and can’t see these legendary gold. Because the center of the rainbow is always on the extension line connecting the sun with your eyes. As you move, the center of the circle moves with it, the rainbow moves, and you can never walk under the rainbow. Moreover, since the position of the rainbow is related to the position of the sun and the eyes of the observer, there is always a slight difference between the rainbow in your eyes and the rainbow in the eyes of others. It is reflected by different water droplets, so the rainbow that everyone sees is actually It is unique.
  Light passing through small droplets
  , however, Aristotle ignored the refraction of light, does not explain why there are multiple rainbow colors, did not calculate the reflection angle of water droplets. It is the French physicist René Descartes who continues this work. Descartes studied the path of light in small droplets.
  He found that light is not only a reflection in small water droplets, but a refraction reflection. Among them, only the incident light that is directly incident into the center of the water droplet completely coincides with the reflected light, while other rays that do not have a direct spherical center are refracted when entering the water droplet: when the inner wall of the water droplet is contacted, the reflection occurs, and when the water droplet enters the air again, Refraction occurs again. Cartesian calculated that the water beam is irradiated on the same side, and after the beam is refracted, reflected, and refracted, the new beam forms an angle of about 42° with the incident beam. Of course, the water droplet is a sphere, so the new beam will form a cone with a vertex angle of 42°.
  Previously, the British physicist Isaac Newton discovered the dispersion phenomenon of light. Through the prism, it can be found that the light is divided into different colors of light, and the different degrees of light deflection are different, among which the red light has the least degree of deflection, and the purple light is biased. The maximum degree of folding. Descartes found that the small water droplets in the sky have the same effect as the prisms. The light of different colors has different angles of refraction and reflection angle in the water droplets. Therefore, after passing through the small water droplets, the light of various colors is separated and formed. The colorful rainbow with fixed color order, the red light is located at the outermost layer of the rainbow due to the small degree of deflection, and the purple light is located in the innermost layer of the rainbow due to the large degree of deflection. The light of other colors will also be due to different degrees of deflection. Finally, they are arranged in a certain order.
  According to Descartes’ model and Newton’s theory, people understand why rainbows are colorful and why rainbow colors are fixed. But sometimes, you will find that there is a bigger rainbow above the rainbow. The color sequence of this rainbow is exactly the opposite of the rainbow color order below. Purple is in the outermost circle and red is in the innermost circle. This bigger rainbow is the neon in the neon.
  Called the rainbow rainbow
  above said, when light enters the water droplets, the occurrence of refraction, reflection, refraction three processes, in fact, in the second refracted light re-exposure to the inner wall of the small water droplets, reflection will happen once this The secondary reflected light is again refracted from the water droplets into the air, eventually forming a neon. To sum up, the rays that form the neon have undergone two refractions and two reflections in the order of refraction, reflection, reflection, and refraction.
  Due to the difference in the degree of refraction, the light that is refracted after the second reflection is exactly opposite to the color of the light directly reflected after the first reflection, so the outermost color of the color of the neon we see is purple, and most The inner layer is red. Descartes calculated that the light that forms the neon forms an angle of about 51° with the incident light, that is, the second refraction of the refraction forms a larger cone of light, so we will find that the neon is in the rainbow. Above, bigger than rainbow. In addition, every reflection of light will lose part of the energy, so the neon formed after two reflections is darker than the rainbow. Among them, Rainbow is also called the main rainbow, and the neon is called the secondary rainbow.
  Having said that, you may think that if the light is reflected in the second refraction and the small water droplets are reflected in the second refraction, and then the neon is formed, then the same will happen in the process of forming the neon. In the case of light, the third and fourth reflections occur, so that the second and third secondary rainbows are obtained. The answer is yes, but in nature, we can only see the phenomenon of neon coexisting, because the energy of natural light is not enough to maintain it after many reflections, we can still observe it. More sub- rainbows need to pass the experiment. Means obtained.
  Looking up at the neon, you will find that the area between the two is relatively dark. This area is called the “Alexander Belt”. It is formed by the light reflected by the small water droplets, which is concentrated below 42° and above 51° at 42°. In the range of 51°, there is almost no light, and this part is much darker than other areas.
  After thousands of years, the pace of people exploring the rainbow has not yet rested. Until now, the rainbow still contains many unknown secrets. For example, why there is a very thin arc under the main rainbow. Explain this phenomenon. Volatility. Past, present, and until the future, scientists will still tirelessly explore the secrets of the rainbow.

  Not the same rainbow
  we see the rainbow after the rain usually rainbow, but in fact, as long as there is enough light, water droplets, appropriate viewing position, no rain could rainbow. Let’s take a look at a few different rainbows.
  Moonbow
  month rainbow, by definition, of course, it is refracted rainbow formed by the moonlight. On the enchanting night of the moon, there are enough small drops of water in the air to form the moon rainbow. However, due to the relatively bright moonlight, the moon rainbow is looming, and our night vision ability is weak, so it is very rare to see the moon rainbow. In fact, the moon rainbow does not necessarily appear in the night, but in the daytime, it is difficult for us to see the moon rainbow that “has a half-faced face.”
  Moonlight usually appears in the sky in the opposite direction of the moon. Before sunrise, the moon is in the west, the moon rainbow will appear in the east; after sunset, the moon is in the east, and the moon rainbow will be in the west. There are currently two famous Moon Red spots in the world, one is the Cumberland Falls in Kentucky, USA; the other is the Victoria Falls between the African Republic of Sembia and Zimbabwe. If you want to see a clearer moon, it is better to go to these two viewing spots.
  Fog bow
  fog bow is formed with a similar rainbow, sun water droplets formed through the reflection and refraction, and a rainbow shape, are arcuate, but fog bow is white, it is called “white rainbow.”
  The reason why the fog rainbow is white is because the droplets forming the fog rainbow are very small, and the diameter is less than 0.05 mm. It cannot function as a scattered light of a triangular prism like a small droplet of a rainbow. The direction of the fog rainbow is the same as that of the rainbow, that is, facing the sun and facing the fog.
  Rainbow Falls
  waterfalls encounter sunlight, can form a rainbow, called “waterfall rainbow.” The formation of the waterfall rainbow is no different from the rainbow.
  If you stand at the top of the waterfall and overlook the entire waterfall, you will be able to see a complete circular rainbow. In many parts of the world, waterfall rainbows can be seen, such as Niagara Falls in North America and Huangguoshu Waterfall in Guizhou, China.
  Homemade rainbow
  In life, we are also able to make a rainbow. Here are two easy ways to do this.
  The first is to put a glass filled with water on the table, and the sunlight can shine on the table through the glass window. Secondly, put a piece of paper, preferably white paper, on the ground so that the sunlight passing through the glass can shine on the paper. Then, spray some hot water on the glass window, then adjust the position of the glass and paper until you see the rainbow.
  Second, the water pipe method. When the weather is fine, turn on the faucet, let the water pipe fill with water, then use your fingers to gently block the nozzle, create a mist, and align the water pipe with the sun to see the rainbow.
  In fact, the easiest way to make a rainbow is to have a sip of water in the sun, with your back to the sun, and you can see the rainbow.