Wonderful natural manuscript information: rainbow

Rainbow is caused by dispersion and reflection caused by sunlight shining on small round water droplets in the air. 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 to 42 degrees is the strongest, which produces the rainbow we see. When this reflection occurs, sunlight enters the water drop, refracts once, then reflects on the back of the water drop, and finally refracts again when it leaves the water drop. Because water has a 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.

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, when the rain clears. At this time, the air is less dusty and full of water droplets, and one side of the sky is dark because of rain clouds. However, observers can see the sunlight without being covered by clouds above or behind them, so rainbows are easier to see. Another place where rainbows are often seen is near waterfalls. When the weather is clear, you can spray water or mist into the air with your back to the sun, or you can make rainbows artificially.

The size of water droplets in the air determines the brightness and width of the rainbow. When the water drops in the air are large, the rainbow is bright and narrow; On the contrary, if the water drops are small, the rainbow will be light and wide. We can't see the rainbow in front of the sun, but only in front of the sun, so the rainbow appears in the west in the morning and always in the east at night. But we can't see it. We can only see it from the sky by plane. The appearance of rainbow is related to the weather change at that time. Generally, we can infer whether it was sunny or rainy from the position where the rainbow appeared in the sky. When there is a rainbow in the east, it is not easy to rain locally, but when there is a rainbow in the west, it is likely to rain locally.

The visibility of rainbow depends on the size of water droplets in the air. The bigger the water drop, the brighter the rainbow, and the smaller the water drop, the less obvious the rainbow is. Generally, in winter, the temperature is low, there are few water droplets in the air, and there is less chance of rain, so there is generally no rainbow in winter.