what causes rainbows

Rainbows are caused by sunlight interacting with tiny water droplets in the air, through refraction, reflection, and dispersion of light inside each droplet.

How a Rainbow Forms

1. Sunlight enters a raindrop (refraction)
   • Sunlight is white light made of many colors (red, orange, yellow, green, blue, indigo, violet).
   • When it passes from air into water, it slows down and bends ; this bending is called refraction.

 * Different colors bend by slightly different amounts because they have different wavelengths, which starts to separate them.

2. Light splits into colors (dispersion)
   • The separation of white light into its component colors is called dispersion.
   • Red bends the least, violet bends the most, so the colors fan out inside the droplet, just like in a glass prism.

3. Light bounces inside the droplet (internal reflection)
   • The refracted light hits the back of the droplet and reflects off the inner surface.
   • This internal reflection sends the light back toward the direction it came from, but now the colors are spread out.

4. Light exits the droplet (second refraction)
   • As the light leaves the droplet and goes back into the air, it bends again.
   • This second refraction further separates the colors and sends specific colors toward your eye at particular angles (around 42° for the bright primary bow).

Why You See an Arc

• You must have the Sun behind you and water droplets in front of you to see a rainbow.
• Each color you see comes from a different set of droplets sending that color toward your eyes at just the right angle, which creates a circular arc centered opposite the Sun.

• From the ground you usually see only part of this circle, so it looks like a bow in the sky.

Primary and Double Rainbows

• A primary rainbow (the common bright one) is formed by light that is refracted, reflected once inside the droplet, and refracted again as it exits.

• A secondary rainbow , which is fainter and appears outside the main one, happens when light reflects twice inside the droplet before leaving.

• Because of the extra reflection, the colors in the secondary rainbow appear in reversed order: red on the inside and violet on the outside.

In short, rainbows are the result of sunlight being bent, split into colors, and reflected inside countless tiny water droplets in the air, then leaving at just the right angles to reach your eyes.

TL;DR: Sunlight enters raindrops, bends and splits into colors (refraction and dispersion), bounces inside (reflection), then bends again as it exits, sending separated colors to your eyes in an arc.

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