Every raindrop is a tiny round window that bends sunlight and fans it into colours. Millions of drops together paint an arc — but only when the sun is behind you.
Most people think a rainbow is a fixed object hanging at a particular place in the sky. In fact it is a relationship between the sun, the rain and your eye, so it shifts as you move and no two people see the same drops.
What's actually happening
A raindrop is a tiny glass bead. Sunlight entering it bends (refraction), bounces once off the back wall (reflection), and bends again on the way out. The bending is what splits the colours: red bends a little less, violet a little more, so each drop fans white sunlight into a tiny spread of colour.
The trick is in the angle. The geometry of a sphere concentrates the exiting light at very nearly one angle — about 42° from the direction of the incoming sunlight for red, 40° for violet. So each drop flashes you exactly one colour, decided by where it sits relative to your eye and the sun. Millions of drops at the 42° ring flash red, drops slightly inside that ring flash orange, and so on down to violet. The "bow" is just that set of rings, drawn in falling water.
Which means a rainbow is not a thing in the sky — it is a relationship between the sun, the rain, and you. Step sideways and your rainbow moves with you; the person beside you sees light from a completely different set of drops. Nobody has ever stood at the end of a rainbow because the end retreats exactly as fast as you walk toward it.
Each raindrop bends, bounces, and bends sunlight again, fanning red out near 42° and violet near 40° — the bow is a circle of drops aimed only at you.
- 1Pick a sunny late afternoon — a low sun makes a taller bow.
- 2Stand with your back to the sun and spray a fine mist from a hose or spray bottle in front of you.
- 3Look about 42° away from your own head's shadow. Move the spray until the arc appears — then take one big step sideways and watch the whole rainbow move with you.
Common questions
A rainbow is not a fixed object but a relationship between the sun, the rain and your eye. As you walk towards it the arc retreats exactly as fast, so the end always stays out of reach.
The fainter second bow, at about 51°, comes from light bouncing twice inside each drop. That extra reflection flips the colour order, and the sky between the two bows looks noticeably dark.
Yes. Any fine spray of droplets works. Stand with the sun behind you and mist the air, then look about 42° from your own shadow to see a private rainbow appear.