What makes a rainbow appear, and why is it curved?

A rainbow appears when sunlight plays hide-and-seek with water droplets in the air, and it curves like a smile because of how light bends as it goes through these tiny drops.

Sunlight is like a bunch of colored crayons all mixed together. When sunlight hits a raindrop, it slows down and bends, this is called refraction. Each color bends just a little differently, so they spread out inside the drop. Then, the light bounces off the back of the drop and comes out again, bending once more as it leaves.

Now imagine you're holding a glass of water, and you shine a flashlight through it, the light changes direction, right? That’s exactly what happens with raindrops, but on a much bigger scale.

Why is the rainbow curved? Because all those raindrops that are doing this bending trick are sitting at just the right angle to your eyes. Imagine lots of little helpers (the raindrops) standing in a circle, each one shows you a different color, and together they make the beautiful curve you see in the sky.