Why do rainbows have only seven colors?

Answer 1

Because "color" is an interaction between the visible light portion of the

electromagnetic spectrum and the light sensitive parts of our eyes.

Our eyes have evolved 4 different receptors--one each for Red, Green and

Blue and another for violet.

A rainbow actually contains millions of colors, but we have evolved to

categorize most of the wavelengths in the visible spectrum as one of the

primary colors and their combinations.

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. If lucky, and a bit superstitious, and

you do find a pot of gold somewhere over the rainbow, please let us know.

After all, we gave you the directions!

Those are the 7 main colors of the light spectrum.

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Answer #2:

They don't. Rainbows have ALL of the colors. Every shade of fabric ever dyed,

every nuance of paint ever mixed, every hue ever perceived by the eye of a

human or any other creature, they're ALL in the rainbow. A huge number of them

have been given names, an even larger number have no names.

But a topic that involves infinities is a bit much to handle in the second grade,

when it's time to start talking about rainbows. So seven colors were selected,

that span the rainbow from end to end, are easy to see in it, and have names

familiar to young children just learning their colors, and that's the way the rainbow is taught.