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What makes a rainbow?

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Why are there so many songs about rainbows, and what's on the other side?

These are the beginning lines of the song, Rainbow Connection, written by Paul Williams and Kenneth Ascher, and sung by Kermit the Frog in The Muppet Movie (1979).

Few visual phenomena in nature excite more than rainbows.

While the image of a rainbow is a visual feast, understanding why rainbows happen can dampen any musings we might have concerning fairy magic and leprechauns with pots of gold at the other end.

And yet, delving into the science of rainbows can yield an even deeper appreciation for the bounty of treats nature has in store for us.

Simply stated, a rainbow depends on two main ingredients to become visible to our naked eye:

  • clear (or 'white') light, and
  • drops of water (a prism)

Humans can see a specific range of colors, where each color corresponds to a specific wavelength. This range of colors is called the 'visible spectrum,' from red being the longest wavelength, to violet, the shortest.

Wavelengths longer than red, or shorter than violet, can not be seen by the human eye. But between, red and violet, humans can see other colors, according to those colors' specific wavelengths.

For a rainbow to appear, light first enters a raindrop. The clear (white) light, comprised of multiple colors, changes, or 'bends,' at different angles, thus separating the (white) light into its component colors, allowing us to see them. A rainbow, thus, is the result of millions of raindrops reflecting and refracting light, and 'exposing' to our eye, specific colors corresponding to specific wavelengths.

Sir Isaac Newton, in 1672, identified five main colors in the rainbow spectrum:

  • red, yellow, green, blue, and violet,
  • but later added orange and indigo.

Needless to say, the unexpected appearance of a rainbow, in all its colorful glory, is a magnificent sight, full of awe and wonder.

A vision? An illusion?

Perhaps it's best to leave the science of angles, refractive light, and wavelength to the brilliant minds that understand the mechanics of nature, while the rest of us devote ourselves to finding our own rainbow connection.

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