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A rainbow is merely a large band of parallel
stripes, blended at the rims, which displays the full
spectrum of colors that make up the  sun's white light. This brilliant
display appears to the naked eye when the sun's light breaks
up as it passes through, the prism-like raindrops
during a rain-shower.
This immense, curved spectrum of light appears only
when both the elements of sunshine and rainfall present. As
the sunlight enters the falling raindrops, it breaks up into
its true colors of red, orange, yellow, blue, and violet.
These colors are always arranged according to their
wavelengths, with red being at one end of the spectrum,
and violet at the other. Once inside the droplet, the
particles of colored light bounce from side to side, reflect
off of the far side of the droplet, exit the droplet, and
reassemble, according to their wavelengths, to form a
rainbow.
Simply because you happen to be in the right place at the
right time, when both elements necessary to form a rainbow are
present, does not mean that you will actually see one. For the
human eye to see these multi-colored bands, ranging from red
to violet, his body must be strategically positioned between
the sun and the rain, with his back to the sun.
If the sun, the eye, and the center of the rainbow's arc
are not in a straight line, the show is over, before it began.
This explains why we only see rainbows in the early morning or
late afternoon…it is physically impossible for us to align our
eyes with the sun at other times of day, as it is high above
our heads! Logically, a morning rainbow appears when the sun
shines in the east, and the rain falls in the west, and an
afternoon rainbow appears when the sun shines in the west, and
the rain falls in the east.
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parallel: 平行的
stripe: 條紋
spectrum: 光譜
prism-like: 象棱鏡一樣的
curved: 彎曲的
wavelength:
波長
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