World Builders™                                                                       Session One  --  Astronomy                                 
The visible spectrum is only a small part of the radiation coming from the sun.

   Like all the other stars, the sun emits radiation. This radiation travels at the speed of light, and includes radio waves, microwaves, infrared light waves, visible light waves (the ones that we can see), ultraviolet light waves, X-rays and Gamma rays.

     Some of these waves are long and of low energy. These waves pass through the atmosphere easily. They can also pass through our bodies, but they do not harm us.

     Some of these waves are short and have very high energy. The strongest of these, gamma rays and X-rays, are called hard radiation. Over-exposure to these waves is harmful to life forms, so we are lucky that they do not pass through the atmosphere to the surface of the earth. Gamma rays are given off by radioactive substances.

     The visible spectrum is a very small part of the radiation that the sun generates. However, the wave lengths that we can see make up the greater part of the radiation that reaches the earth's surface. Both the chlorophyll used by plants and the designs of terrestrial eyes make use of these waves.

Long Wave Length    Low Energy

20 cm to 20 meters

8 inches to 8.5 yards

 Radio Waves  These very long waves are the signals that our radios receive.
 .01 to 21 cm  Microwaves  These long waves cook the food in our microwave ovens.
 700-100,000 nanometers  Infra-red These heat rays are invisible to our eyes.
 400 - 700 nanometers Visible light We see only these wave lengths
 4-400 nanometers  Ultraviolet

Ultraviolet rays are invisible to us, but they cause sunburn.

The ozone layer of the atmosphere protects us from over-exposure to ultraviolet rays.

1-20 nanometers   X-rays The atmosphere protects us from dangerous X-rays. These short, high energy rays can travel right through our bodies, and are used for diagnosis by doctors and dentists. 
smaller than .1 nanometer  Gamma Rays These very short, very high energy waves would kill life on earth if they were able to penetrate the atmosphere.

Short Wave Length              High Energy                   Dangerous to living organisms

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© 1998, 2003. Elizabeth Anne Viau. All rights reserved. This material may be used by individuals for instructional purposes but not sold. Please inform the author if you use it at