Hello

A rainbow is caused by sunlight  and atmospheric condition. Light enters a water droplet ,slowing down and bending as it goes from air to denser water. The light reflect inside of droplet,  separating into into its component wavelength or colours m when light exit the droplet . Rainbow is formed .

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hey

a phenomenon based on refraction. the sunlight (while light) enters water droplet during the rain and the white light is split up by their order of wavelengths and they form a circle (circle bcoz of the sphere of sun). now this circle is seen in the opposite of the direction of sun and is called RAINBOW. the pattern is called VIBGYOR ( violet, indigo, blue, green, yellow, orange, red)

i hope it helps