By: Kate Giere

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Rainbows

• By Kate Giere

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What is a Rainbow?

• A rainbow is typically a multicolored arc that is
  spread across the sky after a rainstorm.
• It usually consists of the following seven
  colors Red, Orange, Yellow, Green, Blue,
  Indigo, and Violet, otherwise known as ROY G.
  BIV
• However, a rainbow also includes a large variety
  of colors, including many that the eye can not
  see.

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Who Discovered the Rainbow?

• In 1637, the formation of rainbows was first
  discussed by Descartes.
• He based his studies on how sunlight reacts with
  one water droplet.

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What Causes a Rainbow?

• A rainbow is caused by light in the atmosphere
  reflecting off water droplets in the air.
• They are also commonly seen near waterfalls.

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Causes of Rainbows cont'd

• The colors seen in a rainbow are caused by the
  dispersion of sunlight through water droplets.
  When sunlight enters a raindrop, or a droplet of
  moisture in the atmosphere, the light is
  refracted at the surface of the drop, then is
  reflected onto the back of the drop, then
  refracted once again as it leaves the drop,
  creating a visible rainbow.

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Why the Same Color Order?

• The color visible is depended on the amount of
  light refracted, and therefore, is dependent on
  the lights wavelength.
• For example, red light has a longer wavelength
  than blue light, and is refracted at a smaller
  angle than the blue light

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Continued...

• Therefore, as the red light enters the drop at a
  smaller angle than blue, it also leaves the drop
  at a smaller angle, and is therefore located on
  the outer part of the rainbow, or the higher part.

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Double Rainbows

• A second rainbow is sometimes visible when there
  is a double reflection of sunlight in the
  raindrop.
• The second rainbow is usually much dimmer than
  the first.
• Because there is a double reflection of this
  light, the colors are inverted, with red on the
  inside (or bottom) and violet on the outside (or
  top).

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Lunar Rainbows

• When there is a full moon, a rainbow can
  sometimes be visible because the bright moonlight
  acts like sunlight as it travels through
  raindrops, producing the rainbow.
• However, this rainbow is usually much fainter
  than one produced by sunlight.

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Interesting Rainbow Facts

• Triple, or even quadruple rainbows are rarely
  seen.
• Rainbows are rarely seen in the winter because
  the water droplets are frozen, which do not
  produce rainbows, but rather scatter light in
  many different patterns.
• Everyone sees a different rainbow, even if they
  think they are looking at the same one, because
  each person sees the light being refracted from
  different raindrops at different angles, which
  creates a different visual rainbow for each
  person.

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Sources

• http//www.geocities.com/grandesmatematicos/Imagen
  es/descartes.jpg
• http//www.eo.ucar.edu/rainbows/
• http//en.wikipedia.org/wiki/Rainbow
• http//www.tahoetwisters.com/NaturePhoto/LargePhot
  os/lg_double_rainbow2.jpg
• http//www.cs.utk.edu/bains/images/Rainbows011.jp
  g
• http//www.fi.edu/color/rainbow.html