Rainbows
A rainbow forms when sunlight enters raindrops, bends, splits into colors, bounces off the back of the drop, and comes out toward your eyes. You need the Sun behind you and rain in front of you.
On this page: how a rainbow forms, why it is curved, why you see colors, and how a second bow can appear.
Read the answer below. In Giant, kids talk with characters and keep the adventure going.
Rainbows
White sunlight is a mix of colors. When it hits a raindrop it slows and bends. That bend is refraction. Different colors bend by different amounts, so the mix spreads. Light reflects inside the drop, then bends again on the way out. Your eyes catch the rays that leave at about 42 degrees from the opposite of the Sun. Lots of drops, same angle, one glowing arc. You cannot walk to a pot of gold. The rainbow moves when you move, because it is a direction, not a place.
~42°
Primary bow angle
2×
Bounces in a second bow
Refraction
Light bends
Sun behind
Where you stand
A rainbow is curved because every glowing drop sits on a cone of the same angle from your eye, and a cone looks like an arc in the sky. From an airplane you can sometimes see a full circle. The ground usually cuts the bottom off, so we get a bow. The curve is geometry, not a painted smile.
A rainbow has colors because each kind of light bends a little differently when it enters a drop. Wavelength is how stretched that kind of light is. Violet bends more than red. The drop spreads them into a fan. We name a famous set: red, orange, yellow, green, blue, indigo, violet. The fan is smoother than seven crayon slots. Your brain groups the smear into familiar names.
Yes. A secondary rainbow happens when light reflects twice inside the drops. It sits higher, is fainter, and the colors flip: red on the inside. The dark band between the bows is called Alexander's band. Spray from a hose can make tiny bows too. Same physics. Smaller stage.
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