Newton Added Indigo to Make Seven Colours

A rainbow appears when sunlight is refracted, reflected and refracted again inside water droplets. The spectrum is continuous, so the number of colours is a matter of naming. Newton settled on seven and inserted *indigo* partly to match the seven notes of a musical scale, which is why generations have struggled to see it.

• An arc of spectral colours in the sky. *A rainbow over the valley.*
• A range of colours or kinds. *A rainbow of options.*
• Rainbow as a modifier. *A rainbow flag.*

Word forms

How it is used in a sentence

• A rainbow always appears opposite the sun.Which is why you see them with the sun behind you.
• The second bow has its colours reversed.From an extra reflection inside the drops.
• Everyone sees a slightly different rainbow.It depends on the position of the observer.

Rainbow facts

• 42 degrees — the angle from the antisolar point where the bow appears
• Double rainbow — a fainter secondary bow with reversed colours
• Alexander's band — the darker sky between the two bows
• Full circle — visible from an aircraft, where the ground does not cut it off
• No fixed position — it moves as you move, so nobody reaches the end

A compound of *rain* and *bow*, in use since Old English. The colour names Newton used in 1704 are red, orange, yellow, green, blue, indigo and violet.