How do rainbows form?
For grown-ups: the science
Rainbows form when sunlight bends, bounces, and bends again inside raindrops, spreading into colors.
A primary rainbow forms when sunlight is refracted on entering spherical raindrops, reflected once from the inner back surface, and refracted again on leaving. Dispersion causes different wavelengths to emerge at slightly different angles. Each observer sees light from a different set of drops, arranged on a cone about 42 degrees from the point opposite the Sun.
What about...?
Ask your child's own question
Transcript
Sunlight glows through raindrops after a shower. How can those tiny drops make a rainbow?
Sunlight enters a round raindrop and bends as it passes from air into water. This bend starts changing the light's path.
Inside the drop, light bounces off the back, then bends again as it leaves. The drop sends the light back toward our eyes.
The colors in sunlight bend by slightly different amounts, so they spread apart. Many drops send these colors together to make a rainbow.
So, sunlight takes a bendy, bouncy trip through raindrops. Each person sees a rainbow made by the drops sending light to their own eyes.