What will the weather be like with a rainbow tomorrow afternoon?

Rainbow is an optical phenomenon in meteorology. When sunlight hits the raindrops in mid-air, the light is refracted and reflected, forming an arched color spectrum in the sky. There are different opinions about the seven colors of the rainbow. The most common scenery in China is (from outside to inside): red, orange, yellow, green, cyan, blue and purple. Western views are: red, orange, yellow, green and purple.

In fact, as long as there are water droplets in the air and the sun shines behind the observer at a low angle, an observable rainbow phenomenon may occur. Rainbow usually appears in the afternoon just after rain. At this time, the air is less dusty and full of small water droplets, and one side of the sky is dark because of rain clouds. However, the observer can see the sun, and there is no cloud on his head or behind him, so the rainbow will be easier to see. Another place where rainbows are often seen is near waterfalls. When the weather is clear,

Night rainbow is a rare phenomenon, which may appear in the night with strong moonlight. Because it is difficult for human vision to distinguish colors in the weak light at night, the night rainbow looks as if it is all white.

principle

The optical principle of rainbow is that sunlight shines on small round water droplets in the air, resulting in dispersion and reflection. When sunlight enters the water drop, it will be incident at different angles at the same time and reflected at different angles in the water drop. The reflection of 40-42 degrees is the strongest, which produces the rainbow we see. When this reflection occurs, sunlight enters the water drop, refracts once, and then reflects on the back of the water drop. Finally, it refracts again when it leaves the water drop. Because water has dispersive effect on light, the refractive index of light with different wavelengths is different, and the refractive angle of blue light is greater than that of red light. Because light is reflected in water droplets, the spectrum seen by the observer is reversed, with red light at the top and other colors at the bottom.

Double rainbow, neon above, rainbow below. Many times, two rainbows appear at the same time, and a concentric but darker secondary rainbow (also called neon) appears outside the ordinary rainbow. The secondary rainbow is formed by two reflections of sunlight in water droplets. The strongest reflection angle of the two reflections occurs at 50 to 53, so the secondary rainbow is located outside the main rainbow. Because of the two reflections, the color order of the secondary rainbow is opposite to that of the main rainbow, and the outside is

The rainbow does not actually appear in a specific position in mid-air. What the observer sees is an optical phenomenon. The position of the rainbow will change with the observer. When an observer sees a rainbow, its position must be in the opposite direction of the sun. The center inside the rainbow arch is actually an enlarged image of the sun reflected by water droplets. So the sky inside the rainbow is brighter than the sky outside the rainbow. The center of the rainbow arch is just in the direction of the observer's head shadow, and the rainbow itself is 40 to 42 degrees above the line between the observer's head shadow and his eyes. Therefore, when the sun is higher than 42 degrees in the sky, there will be no rainbow below the horizon. This is why rainbows rarely appear at noon.

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The rainbow extends from one end to the other. With an ordinary 35mm camera, you need a wide-angle lens with a focal length below 19mm to capture the whole rainbow in a single frame. If you are on an airplane, you will see that the rainbow is a complete circle instead of an arch, and the center of the circular rainbow is the direction of the airplane.

In 1307, it was suggested in Europe that rainbows are caused by the refraction and reflection of sunlight by water droplets. Descartes found in 1637 that the size of water droplets does not affect the refraction of light. He experimented with water injected into glass balls and got the refractive index of water. Mathematically, it is proved that the main rainbow is caused by reflection in the water point, while the auxiliary rainbow is caused by two reflections. He calculated the angle of the rainbow accurately, but failed to explain it.

Later, Newton discovered all the optical principles of rainbow formation after scattering sunlight into color with a glass rhombus.