We see rainbows because sunlight is bent, split into colors, and reflected inside tiny water droplets in the air, then sent back to our eyes at just the right angles.

What a rainbow actually is

A rainbow is not a physical “thing” in the sky, but a visual effect created by countless raindrops acting like tiny prisms. Each droplet takes white sunlight and turns it into a mini spectrum of colors, and you see a bright arc where many of those colored rays line up toward your eyes.

The three key light tricks

Inside each raindrop, sunlight goes through three main steps:

  1. Refraction (bending in)
    • Light slows and bends as it enters the water droplet from air.
 * Different colors bend by slightly different amounts, so they start to separate (dispersion), like in a glass prism.
  1. Internal reflection (bouncing inside)
    • The light hits the back of the droplet and some of it reflects off the inner surface.
 * This bounce turns the light back toward the front of the droplet, roughly in the direction it came from.
  1. Refraction again (bending out)
    • When the light exits the droplet, it bends a second time and the colors spread out more.
 * For the primary rainbow, the strongest outgoing rays reach your eye at about 42 degrees from the direction opposite the Sun.

Why we see colors in order

Because different colors bend by different amounts, they leave the droplet at different angles.

  • Red light bends the least, so it appears on the outer edge (top) of the primary rainbow.
  • Violet bends the most, so it appears on the inner edge (bottom).
  • The familiar sequence (red, orange, yellow, green, blue, indigo, violet) comes from that smooth spread of wavelengths.

To your eye, the sky looks like it has colored “stripes,” but it’s really a continuous gradient of wavelengths.

Why the Sun and your position matter

You only see a rainbow when your eye, the raindrops, and the Sun line up in a very specific way.

  • The Sun must be behind you, usually low in the sky (morning or late afternoon).
  • Raindrops (or mist, spray, or fog droplets) must be in front of you.
  • Your line of sight toward the rainbow is centered on the point opposite the Sun, called the “antisolar point.”

Because the geometry depends on your eye, every person actually sees their “own” rainbow formed by a different set of droplets. Move a few steps and the specific droplets sending you red or blue light change, even though the arc looks the same.

Double rainbows and other twists

Sometimes conditions produce extra or unusual rainbows.

  • Double rainbows: If light reflects twice inside the droplets, you get a fainter second arc above the main one.
* Its colors are reversed: red on the inside, violet on the outside.
  • Fogbows: In very fine droplets (like fog), the “rainbow” can appear very pale or almost white, because colors don’t separate as clearly.
  • Sprinkler or waterfall rainbows: Garden hoses, fountains, and waterfalls all throw tiny droplets into the air, creating smaller, nearby rainbows with the same physics.

You can think of every raindrop as a microscopic prism and mirror, quietly splitting and redirecting sunlight to paint color into your field of view.

Information gathered from public forums or data available on the internet and portrayed here.