A rainbow over the 1975-76 Tolbachik eruption: Kamchatka Krai, Russia

A rainbow near the Nashi pear tree in the bloom

A rainbow is an arc of colour in the sky that can be seen when the sun shines through falling rain. The pattern of colours, called a spectrum, starts with red on the outside and changes through orange, yellow, green, blue, indigo, and violet on the inside. Sometimes a second, larger, dimmer rainbow is seen.