Rainbows: A Spectrum of Light

Visible light is a small part of the electromagnetic spectrum. Radio waves are the longest waves and lowest frequency waves on the spectrum. The length of the waves decreases and the frequency increases as we move up the spectrum. The radio waves are followed by microwaves and then infrared. Infrared is followed by visible light, ultraviolet, x-rays, ending with gamma rays. Gamma rays have the shortest wavelengths and the highest frequency. The energy of the wave is directly proportional to its frequency.

Visible light is the dividing line between the ionizing, harmful electromagnetic ways, and non-ionizing radiation. We are constantly bombarded with radio waves, microwaves, infrared and visible light. They are essentially harmless.

Ultraviolet rays, x-rays, and gamma rays are another story. They are classified as ionizing radiation. Simply put, they can and do destroy living tissue. A constant dose of low level ionizing radiation can have devastating long term affects. Is that golden tan really worth it? (Exposure to visible light does not produce the sunburns or the tans. It's the Ultraviolet light.)

All electromagnetic waves travel at 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.

. 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.

Rainbows can be seen whenever there are water droplets in the air and the sun is shining from behind you. The water droplets act as a prism bending the light into its bands of color. The most spectacular displays occur with the sky is still dark with dissipating clouds. I understand why our ancestors thought they were magical.

Throughout human history rainbows have been a symbol of hope. The storm is passing. The sun will shine again. We dream. If we follow our dreams, like the rainbow, and we will find that pot of gold hidden in the light.