..... Click the link for more information. , 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 refraction, in physics, deflection of a wave on passing obliquely from one transparent medium into a second medium in which its speed is different, as the passage of a light ray from air into glass.
..... Click the link for more information. and reflection reflection, return of a wave from a surface that it strikes into the medium through which it has traveled. The general principles governing the reflection of light and sound are similar, for both normally travel in straight lines and both are wave phenomena.
..... Click the link for more information. 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 Descartes, René , Lat. Renatus Cartesius, 1596–1650, French philosopher, mathematician, and scientist, b. La Haye. Descartes' methodology was a major influence in the transition from medieval science and philosophy to the modern era.
..... Click the link for more information. 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 Inca , pre-Columbian empire, W South America. The name Inca may specifically refer to the emperor, but is generally used to mean the empire or the people. Extent and Organization of the Empire
..... Click the link for more information. 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).
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.
rainbow
rainbow [′rān‚bō]
Rainbow
an optical phenomenon of the atmosphere that resembles a multicolored are in the sky. A rainbow is observed when solar rays shine on water droplets that are in the part of the sky opposite the sun. The center of the are of a rainbow is located on a straight line that passes from the solar disk to the observer’s eye; that is, the center is at a point opposite the sun. The are of a rainbow is the part of a circle circumscribed around this point with a radius of 42° (see Figure 1).
The color sequence in a rainbow is the same as in the solar spectrum. Red is usually located on the outside edge of the bow, and violet is usually on the inside edge. Secondary rainbows, which border on the main arc, are sometimes visible from the inside edge. The visible part of the rainbow are is determined by the sun’s position; when the sun is on the horizon, a rainbow is a semicircular are; as the sun rises, the visible part of the are decreases; and when the sun is at an altitude of 42°, the rainbow disappears.
A phenomenon similar to the rainbow may be observed in the spray of fountains and waterfalls. Moonbows and rainbows created by artificial light sources also occur. A secondary rainbow is frequently observed that has an angular radius of about 52° and a reversed color sequence.
The first rainbow theory was proposed in 1637 by R. Descartes. A more exact theory was developed in 1836 by the British astronomer G. Airy and in the late 19th century by the Austrian geophysicist I. M. Pernter. This theory is based on calculating the diffraction and interference effects that accompany the encounter of solar rays with the curtain formed by raindrops.
REFERENCE
Minnaert, M. Svet i tsvet v prirode. Moscow, 1958. (Translated from English.)Want to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit the webmaster's page for free fun content.
| ?Page tools | ||
|---|---|---|
|