An Etymological Dictionary of Astronomy and Astrophysics

A color effect produced by the → refraction and → internal reflection of sunlight passing through a mist of tiny spherical water → droplets in the air. The effect is visible only when the observer has his back to the Sun.
It appears as a colored band at about 138° from the Sun, hence 42° from the → antisolar pint. In other words, 42° is the angle between the direction of the → incident sunlight and the → line of sight.

The → primary rainbow is caused from one reflection inside water droplets; the red color appears on the top and violet on the bottom.

At solar elevations higher than 42° the bow is entirely below the → horizon and therefore invisible in the sky.

A full rainbow is actually a complete circle, but from the ground we see only part of it. From an airplane, in the right conditions, one can see an entire circular rainbow.

A → secondary rainbow appears if the sunlight is reflected twice inside the water droplets. Secondary rainbows are fainter, and the order of the color is reversed, with red on the bottom and violet on the top.
See also: → Alexander’s dark band, → supernumerary rainbow.

See also: From → rain; → bow.