What Causes a Rainbow
Rainbows are a natural optical phenomenon that occurs when sunlight passes through raindrops in the atmosphere. As light enters a raindrop, it slows down and bends a process called refraction. Then the light reflects off the inside surface of the drop and refracts again as it exits. This bending and reflecting separates the white sunlight into its component colors red, orange, yellow, green, blue, indigo, and violet. This is why we see a rainbow as a spectrum of colors arranged in a beautiful arc.
Why Do Rainbows Have an Arc Shape
The arc shape of a rainbow is due to the consistent angle at which the light is bent and reflected inside each raindrop. The primary rainbow appears at an angle of about 42 degrees from the direction opposite the sun. This angle creates a circular pattern, but we usually see only the top half of the circle because the ground blocks the rest. In rare cases, such as from an airplane or high mountain, a full-circle rainbow can be seen. This consistent geometry and the alignment of millions of tiny raindrops create the familiar rainbow shape we all recognize. Shutdown123