RAINBOW

(Meteorology) A circular bow or arc exhibiting, in concentric bands of light, the several colors of the spectrum, and formed opposite the sun by the refraction and reflection of the sun's rays in drops of rain. Also, a similar arc may be formed by the moon, or some other source of light, or one formed in spray mist, fog, clouds, etc. Rainbows are circular because the drops, being spherical, are alike in every position. In the case of the ordinary rainbow, or Primary Rainbow, the effective rays are refracted on entering each drop, reflected from its interior surface and refracted again on emerging, then passing to the observer's eye. The red is seen on the outside edge of the bow. Also, there is often seen another larger bow, the Secondary Rainbow, concentric with and near the first. Its formation differs from that of the primary rainbow in that there are two internal reflections, it is much fainter, and it has the red on the inside edge. Faint-colored arcs sometimes seen next to the primary or secondary bow, due to interference, are Supernumerary, or Spurious, Rainbows. White Rainbows are sometimes formed by fog or clouds, but are too minute to give distinctly the concentric bands of color of the ordinary rainbow.