rainbow

rainbow, arc showing the colors of the spectrum, violet inside and red outside, which appears when the sun shines through water droplets. It often appears while the sun is shining after a brief thundershower in the late afternoon or on fog layers. The sun, the observer's eye, and the center of the arc must be aligned—the rainbow appears in the part of the sky opposite the sun. The rainbow is an arc of 180° if the sun is at the horizon, and it cannot appear if the sun is high in the sky. It is caused by the refraction and reflection of rays from the sun on a "sheet" of water droplets. The light is refracted as it enters the sphere of the individual water drop, then is reflected from the drop's opposite side, and is again refracted as it leaves the drop and passes to the observer's eye. When conditions are suitable, a double rainbow may be seen; a larger, paler, secondary rainbow with colors reversed (red inside) outside the primary arc is caused by two refractions and two reflections of the ray while it is inside a drop. The "rainbows" of mist, lawn spray, and spray from a waterfall are similarly caused. The lunary rainbow, seen much less often, is usually observable soon after dark following a brief summer storm or shower when the moon is nearly full. Aristotle was first to devote serious attention to the rainbow, but his mistaken explanation of it misled thinkers for centuries. Descartes in the 17th cent. also attempted to account for the phenomenon but the correct explanation of it could not be furnished until the physics of light and its reflection and refraction were understood and the spectrum explained. In religion and art the rainbow symbolizes God's promise of mercy to mankind after the Deluge (Gen. 9.13). The Greeks and Romans called the rainbow the sign of Iris, messenger of the gods. The Inca and other Native Americans regarded the rainbow as a gift from the sun-god. There are fairy tales of searches for the pot of gold at the foot of the rainbow.

Bibliography

See R. Greenler, Rainbows, Halos, and Glories (1990).

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rainbow

Series of concentric, coloured arcs that may be seen when light from a distant source—usually the Sun—falls on a collection of water drops such as in rain, spray, or fog. The coloured rays of the rainbow are caused by the refraction and internal reflection of light rays that enter the drop, each colour being bent through a slightly different angle. Hence, the combined colours are separated upon emerging from the drop. The most brilliant and most common rainbow is the so-called primary bow, which results from light that emerges from the drop after one internal reflection. The colours of the arc (from outside to inside) are red, orange, yellow, green, blue, indigo, and violet. Occasionally a less-intense secondary bow may be observed; it has its colour sequence reversed.

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Rainbow

Digital Equipment's original offering in the PC market. The Rainbow, released between 1982 and 1986, used an Intel 8088 to run MS/DOS, but could also run CP/M programs because its Z80 keyboard processor served as an alternate CPU. The Rainbow was not hardware-compatible with the IBM PC.

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rainbow

1. a bow-shaped display in the sky of the colours of the spectrum, caused by the refraction and reflection of the sun's rays through rain or mist

2. of or relating to a political grouping together by several minorities, esp of different races

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rainbow [′rān‚bō]

(electronics)

Technique which applies pulse-to-pulse frequency changing to identifying and discriminating against decoys and chaff.

(optics)

Colored arc seen in the sky when the sun or moon is illuminating large numbers of falling raindrops.

(petroleum engineering)

Chromatic iridescence observed in drilling fluid that has been circulated in a well, indicating contamination or contact with fresh hydrocarbons.

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rainbow

God’s assurance He would not send another great flood. [O.T.: Genesis, 9:12–16]

See : Hope