The weather of Yunyantou Bridge

The answer is rainbow. The wind stopped raining, and there was a colorful bridge on the horizon. There were no horses and chariots running on the bridge and no white sails floating under it. This is the rainbow after the rain.

Rainbow, in fact, as long as there are water droplets in the air and the sun shines behind the observer at a low angle, it may produce an observable rainbow phenomenon. Rainbow usually appears in the afternoon, just after the rain. At this time, the air is less dusty and full of water droplets, and one side of the sky is dark because there are still 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 create an artificial rainbow.

Extended data:

The principle of rainbow

Rainbow is formed by the scattering and reflection of sunlight on spherical 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 kind of reflection is caused, the sunlight enters the water drop, refracts once, then reflects on the back of the water drop, refracts again when leaving the water drop, and always refracts twice after one reflection.

Because water has a dispersive effect on light, the refractive index of light with different frequencies is different. The refractive index of red light is smaller than that of blue light, and the deflection angle of blue light is larger 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.