Why do rainbows appear in sunny weather after rain?

Rainbow appears on a sunny day after rain, which is an optical phenomenon after rain. When sunlight hits the water droplets in mid-air, the light is refracted and reflected, forming an arched color spectrum in the sky.

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. 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.

Rainbow usually appears in the afternoon, when the rain clears. At this time, the air is full of small water droplets with less dust, and one side of the sky is dark because there are still rain clouds, but the sun can still be seen without the cover of clouds above or behind the observer. When the sun shines behind the observer at a low angle, it may produce an observable rainbow phenomenon.

Extended data:

Reflection rainbow and reflection rainbow phenomenon after rain;

1. When a rainbow appears on an object on the water surface, two mirror arcs with complementary optical paths may appear on the water surface and under the water surface respectively. If the water surface is calm, the reflected rainbow will appear as a mirror image below the horizon of the water surface. Sunlight is deflected by raindrops before reaching the observer, and then reflected by water. Even in small puddles, reflected rainbows, at least in part, are often visible.

2. When the sunlight is reflected by the water surface before it reaches the raindrops, it may produce a reflected rainbow. If the water surface is large enough, the whole water surface is calm and close to the rain curtain, the reflected rainbow may appear on the horizon. It meets the normal rainbow at the horizon, and its arc will be higher in the sky because its center is above the horizon, while the center of the normal rainbow is below the horizon.

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