If light travels in a straight line, how come a curved rainbow can be seen in a mist or rain? With a prism, the light also breaks up rectilinearly into its color spectrum, right?
Answer
Dear Tjarko,
For example, if we ‘see’ a table in the sun, this means that light travels from the sun to the table, is reflected there, goes to our eye and hits our retina. Then an unconscious complex calculation happens in our brain and then we know that there is a table in a certain position with certain properties. When we think we ‘see’ a rainbow, it is an illusion because there is only water vapor in that place on which light is reflected in different colors. When we see a rainbow, light from the sun travels to a raindrop, bounces off it and hits our eye. If a wide beam of light falls on a raindrop, there is reflection in all directions. The direction in which a raindrop reflects the most light is between 40 and 42 degrees. If you see a rainbow from an airplane on a lower cloud, you see the shadow of the airplane in the center of the circle. The circle itself is formed by all possible places where reflection is possible at an angle of about 40 degrees, so all possible drops so that the angle sun-drop-eye is about 40 degrees. This maximum reflection angle depends on the color of the light (see figure). White light is a mixture of all colors of light. Blue light has the smallest reflection angle and is therefore inside the circle. Red is outside.
Answered by
ir. bruno Bauwens
Computer Sciences
http://www.ugent.be
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