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Rainbow,
arch of light exhibiting the spectrum colors in their
order, caused by drops of water falling through the air.
It is seen usually in the sky opposite to the sun at the
close of a shower and also in the spray of waterfalls. In
the brightest or primary bow, often the only one seen, the
colors are arranged with the red outside. Above the
perfect bow is a secondary bow, in which the colors are
arranged in reverse order; this bow is dimmer, because of
a double reflection within the drops.
When the sunlight enters
a raindrop it is refracted, or bent, by and reflected from
the drop in such a way that the light appears as a
spectrum of colors.
The colors can be seen,
however, only when the angle of reflection between the
sun, the drop of water, and the observer's line of vision
is between 40° and 42°.
When the sun is low in
the sky the rainbow appears relatively high; as the sun
rises higher, the rainbow appears lower in the sky,
maintaining the critical 40°- to 42°-angle. When the sun
is more than 42° above the horizon no rainbow can be seen
because the required angle passes over the head of the
observer.
This
information has brought it to you from Encarta 2002
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