Rainbow From Light
by Jeanette Cain
Rainbow in morning, sailor take warning;
Rainbow at night, sailor's delight.
Rainbow to windward, foul fall the day;
Rainbow to leeward, damp runs away.
Sailors once used this little rhyme to sail the open oceans. A rainbow, like other unknown events, such as, eclipses and aurora, were the cause of many superstitions. With accurate observations science has made accurate explanations of the old superstitions and added to the knowledge of science.
What causes a rainbow?
Light has a behavior, which means that it behaves to a few simple principles. These principles were discovered through observation. When a certain set of circumstances occur, they produce a certain effect, which can be predicted. From these principles we can explain mysterious light phenomena, such as, images in mirrors, shadows, mirages, brightness and color. The greatest benefit from these discoveries is the ability to correct bad vision, create photographs and movies of people, places, and things.
Reflection is responsible for making nonluminous objects and materials visible. Any object will reflect some light falling upon it, but some reflect more than others. Most give a diffuse reflection and send light in many directions. It is through this principle that we see and observe texture, color, and the ability to distinguish objects from their surroundings. There are highly
polished materials, like silver, aluminum and steel that reflect in a regular manner compared to the rougher surfaces of some objects.
What is the behavior of reflected light?
Does light travel in straight lines? You decide. Try this experiment:
1. Take 3 cards with a hole punched in each one.
2. Make adjustments to the cards until a beam of light from a flashlight shines through all 3 holes in a consecutive set-up. You will need to create something to keep the cards straight and standing on a table or other surface.
3. Turn off the flashlight and look through the 3 holes.
Did you prove that light travels in a straight line? Can you think of a better way to prove this?
You may have thought of something similar to the following example.
When you look at a tree, you are able to see the tree because the light travels in a straight line-from the tree to your eye. If the tree is to the south, walk with your eyes closed. You will probably bump into the tree. Does this convince you that light travels in a straight line? Could you simplify the example? Is it not correct to say that if we start with a reasonable assumption, which is that light travels in a straight line, then you can use this for all explanations and predictions concerning light? If this does not lead you to a contradiction and a mistake, does it make your assumption correct? Can you think of other possible examples?
1. Editors. The World Book Encyclopedia. World Book-Childcraft International, Inc: Chicago. 1990
2. Kennon, William L. Astronomy: A Textbook for Colleges. Ginn and Company: Boston. 1968.
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