Rainbella

Meet Rainbella, a raindrop with a rainbow behind her.

Sunlight entering a raindrop bends, reflects once off the back of the drop, and bends again on the way out. Because the amount of bending depends slightly on wavelength, the colours separate. Light leaving drops is concentrated at about 42° from the antisolar point, the point directly opposite the Sun, so each colour forms a circle there. René Descartes worked out the 42° angle in 1637, and Isaac Newton later explained the colours.

Since the bow is centred opposite the Sun, its top sits at 42° minus the Sun's height. With the Sun 30° above the horizon, the top of the bow is only 42 − 30 = 12° up. If the Sun is higher than about 42°, no main bow can be seen from the ground.

That is why rainbows appear in the morning or late afternoon, with the Sun behind you. A fainter secondary bow at about 51° has its colours reversed, from two reflections inside each drop.

Each observer sees a different rainbow, made by different drops. Red is on the outside, violet inside.