What Causes a Rainbow

A rainbow is one of the most colorful and beautiful sights in the sky. It appears when sunlight shines through water droplets in the air, usually after it rains. But how does light turn into a rainbow of colors? The answer lies in how light bends and reflects.

Sunlight may look white, but it is actually made up of many different colors—red, orange, yellow, green, blue, indigo, and violet. When sunlight enters a water droplet, it slows down and bends. This bending of light is called refraction. Each color bends a little differently because of its wavelength, which is why the colors spread out.

Inside the droplet, the light bounces off the back and travels back out, bending again as it leaves the droplet. This second bending helps separate the colors even more. The process of light bouncing inside the droplet is called reflection.

When millions of water droplets reflect and bend sunlight at the same time, a circular arc of colors appears in the sky. The colors always follow the same order: red on the outside, and violet on the inside.

You can only see a rainbow if the sun is behind you and the rain is in front of you. Rainbows are most common in the morning or late afternoon, when the sun is lower in the sky.

Fun Fact: A rainbow is actually a full circle, but from the ground, we can only see the top half. From an airplane, you might see the whole circle!