Why are rainbows semicircle not other shapes?

Answer 1

A rainbow just appears as a semicircle but it is actually a complete circle. We just don't see the whole thing because the horizon gets in the way. Sometimes people on planes will see the entire circle with the shadow of the plane in the center.

White light is made up of a mixture of all the different colors. Light takes the form of waves and all the different colors have a different wavelength. Red light has the longest wavelength (720 nm) while violet has the shortest (380 nm). These different wavelengths can be used to explain why you see all the different colors in the rainbow. When light hits water droplets in the air, it is bent slightly - this bending is called diffraction. The amount of diffraction depends on the wavelength - Red light is bent less than blue light so when white light meets the water droplets, it is separated into all the different colors.

If you turn on a garden hose, adjust the nozzle to a fine spray and stand with your back to the sun, you will see a rainbow shining in the spray!

Answer 2

Rainbows appear as a semicircle because they are formed by the refraction, reflection, and dispersion of sunlight in raindrops. The half-circle shape is a result of the angle at which light is refracted inside the spherical raindrop. The dispersion of light into its colors creates the distinct arc shape that we see.