Why do rainbows appear on clouds?

Bending reason: In fact, if the conditions are right, you can see a whole circle of circular rainbow (such as the Buddha's light in Emei Mountain). When this kind of reflection is formed, 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 finally hits people's eyes. The bending degree of light passing through water drops depends on the wavelength (i.e. color) of light-red light has the largest bending degree, followed by orange light and yellow light, and so on, and violet light has the smallest bending degree. 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. Each color has a specific bending angle. The refraction angle of red light in sunlight is 42 degrees, while that of blue light is only 40 degrees, so each color appears in a different position in the sky. If an imaginary line is used to connect the back of the head with the sun, then the place that makes an angle of 42 degrees with this line is where the red color is. These different positions outline an arc. Since the angle between the blue and the imaginary line is only 40 degrees, the blue arc on the rainbow is always below the red.