Interactive Explainer
How do rainbows form?
A rainbow appears when sunlight enters many raindrops, bends, reflects inside, and emerges separated into colors. You only see it when the geometry is right: Sun behind you, droplets ahead of you, and the Sun not too high.
Rainbows are made by refraction, internal reflection, and dispersion inside countless droplets, not by colors being painted onto the sky.
Low Sun, bright droplets, and a darker background often make the arc appear stronger and easier to notice.
Red appears on the outer edge of a primary rainbow and violet on the inner edge because different wavelengths leave the drop at slightly different angles.
Try It Yourself
Rainbow Lab
Lower the Sun, thicken the spray, enlarge the droplets, or darken the cloud background to see when a rainbow sharpens, widens, or disappears entirely.
What changes the fastest
What is driving the result
The Big Idea
What is actually happening?
An interactive explainer about how raindrops bend and separate sunlight, why rainbow colors appear in a fixed order, and why a second rainbow flips the colors.
Sunlight enters the droplet
As the light crosses from air into water, it bends because it is moving into a different medium.
Colors spread slightly apart
Different wavelengths bend by slightly different amounts, so white sunlight begins to separate into a spectrum.
Light reflects inside the drop
Some of the light bounces off the back of the droplet and heads back toward the front.
Only the right exit angles reach you
You see a rainbow when many droplets send different colors back toward your eyes at the correct angles.
Good Follow-Up Questions
The details are where this gets interesting
The short answer helps, but the edge cases and comparisons are what make the topic memorable.
A rainbow is not in one fixed place
It depends on the line between you, the Sun, and the droplets. Move, and you are effectively seeing a different set of droplets contribute the bow.
Secondary rainbows reverse the colors
A second internal reflection inside the drop can produce a dimmer outer bow with the color order flipped.
You can see a full circle from above
From the ground, the horizon usually cuts the bow off. From an airplane or mountaintop with droplets below you, a full circle is possible.
Compare Scenes
Why one rainbow is faint and another seems to jump off the sky
Sun angle, droplet field, and the background behind the arc all change how dramatic the bow looks.
Fast Answers
Questions people usually ask next
Good science pages should answer the obvious follow-ups without making the reader hunt for them.