How are rainbows made?

Rainbows appear when raindrops (similar to a prism) reflect sunlight, thus breaking white sunlight into colors.

How is light reflected to create rainbows?

As light enters a water droplet, the different wavelength colors bend at slightly separate angles. Some of this light reflects off the back of the droplet and is bent a second time as the droplet emerges from the light beam. Drops at different angles send distinctively different colors to the eye.

If light is hitting raindrops at a proper angle, a secondary, larger rainbow will appear outside of the main rainbow. This secondary rainbow is fainter in color than the main one because the light has been reflected twice by each raindrop. This double reflection also reverses the colors in the secondary rainbow.

To see a rainbow, an observer must have her back to the sun and rain must be falling in some part of the sky. Since each raindrop is lit by the white light of the sun, a spectrum of colors is produced.

No two observers will ever witness exactly the same rainbow because each will view a different set of drops at a slightly different angle. Also, each color seen is from different raindrops.