MOMENTARY BRILLIANCE

The sight of a single rainbow arching across the sky is usually enough to draw gasps of wonder. A double rainbow is even more impressive and less frequently seen. It forms when light reflects off the back of a raindrop twice. Different colours of light bend at different angles, creating the spectrum as we see it. In the double rainbow, raindrops which are higher in the sky reflect violet light and those which are lower reflect red light, so the order is inverted, with indigo at the top of the rainbow and red underneath. The dark band between is known as Alexander’s band, after Alexander of Aphrodisias, an ancient Greek commentator who first described it. Double rainbows are most often seen when the sun is low in the sky, with the perfect arc occurring only at sunrise or sunset.