Weather & seasons · Light and water droplets
Why does a rainbow shine?
A colourful arc sends Puschel looking for an answer instead of treasure.
The short answer
Water drops bend sunlight and reflect some inside. This separates its colours. With the Sun behind and drops ahead, you may see a rainbow. It is an effect of light, not a solid coloured object.
Follow the sunlight
1. Sun behind, drops ahead
The Sun is behind the observer and the drops are ahead. The yellow arrow shows light travelling to the drops. The returning arrow stands for light reaching the eye from a suitably placed drop.
2. Light bends and reflects
One round drop is enlarged. Follow the arrow from the left: light changes direction as it enters. At the back inside surface, some light is reflected. It changes direction again as it leaves.
3. Colours leave at different angles
Sunlight contains many colours. The drop bends them by different amounts. Red and violet show two light paths as they leave. Not all colours from the same drop reach your eye at once.
Refraction means light changes direction as it passes between air and water. Reflection means light is sent back at a boundary.
One drop does not supply a complete coloured bow. Very many drops in suitable directions send light to your eyes; together they form the primary rainbow with red outside and violet inside.
The drawing shows selected paths, not all reflections; sizes are simplified and the two coloured exit paths are spread apart for comparison. Never look into the Sun.
Why do we see a colourful rainbow rather than just bright sunlight?
Water drops redirect sunlight and separate its colours. Light is refracted as it enters and leaves, and reflected inside. Coloured light from many suitably placed drops reaches your eyes. The Sun is behind you. The bow is a light effect, not a solid coloured bridge.
An imagined Wusel scene
Puschel and Flauschi investigate
Puschel“The colour ends over there!” calls Puschel. Flauschi stays on the path. Flauschi“We can see it, but cannot collect its end like an object.”
Puschel looks more closely. Instead of rigid stripes he notices gentle colour transitions. His treasure idea becomes a question about light.
Puschel“Then I will take a memory,” he says. Flauschi nods. That fits even in an empty paw.
Little Wusel quiz
Can you reach and touch a rainbow’s end?
Show answer
No. It is an optical effect whose apparent position depends on our viewpoint.
Explore in more detail
Here you will find longer explanations and further details. You can explore them together.
Understand step by step
How it works – simply explained
Sunlight reaches drops
In an ordinary sunlight rainbow the Sun is behind you and water drops ahead.
A drop changes light paths
Entering light refracts differently by colour, reflects inside, then refracts again on leaving.
Your position sets the arc
Light from suitable directions reaches your eyes as an arc, red outside and violet inside. It is not a solid object with a walkable end.
Why a rainbow depends on where you stand
Suitable droplets direct light to your eyes at suitable angles. Moving changes which droplets match those angles. The visible rainbow therefore depends on your position, not a painted bridge you can touch. A single droplet redirects light; an actual visible rainbow involves many droplets.
References for this explanation: [1]
The key points again
Discover
A rainbow forms as light is refracted and reflected inside water droplets. This separates its colours.
Understand
For an ordinary solar rainbow the Sun is behind us and the droplets are in front.
Connections
The primary rainbow has red on the outside and violet on the inside. Its apparent position depends on the observer’s viewpoint.