The Speed of Light

The speed of light traveling in a vacuum is currently defined as 299,792,458 meters per second. That is approximately 186,282 miles per second. Note: The speed of light is dependent on the medium through which it travels. Its speed is lower when moving through transparent substances such as glass or water. When crossing a boundary between one substance and another, the speed of the light wave changes but the frequency does not. Consequently the wave bends. How far it bends depends on the length of the wave. It is this feature that makes a rainbow possible.

Visible Light and the Colors of a Rainbow

A very small portion of the electromagnetic spectrum is actually visible to the human eye. Red light has a wavelength of approximately 380 to 400 nanometers. As we move up the spectrum, the wavelength decreases. Violet has a wavelength of approximately 700 to 750 nanometers. The length of the wave determines how much it bends when it enters or exits a prism. The longest wavelength (red) bends the most. Orange bends a little less, followed by yellow and on down the line.

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That's why the order of color in the rainbow does not vary. Red (the longest wavelength) will always be on top with violet (the shortest) on the bottom.