170 Common Science 



lake or an ocean, you can notice it decidedly when you 

 look straight down into the water itself. 



When you look at a smooth body of water at a slant 

 on a clear day, the blue sky is reflected to you and the 

 water looks blue instead of green. And it may even 

 look blue when you look straight down in it if it is too 

 deep for you to see the bottom and the sky is reflected 

 from the surface. 



Why the sky is often red at sunset. Dust lets more 

 of red and yellow light through than of any other color, 

 and for this reason there is much red and yellow in the 

 sunset. Just before the sun sets, it shines through the 

 low, dusty air. The dust filters out most of the light 

 except the red and yellow. The red light and yellow 

 light are reflected by the clouds (for the clouds are 

 themselves " white " ; that is, they reflect all the colors 

 that strike them), and you have the beautiful sunset 

 clouds. Sometimes there is a purple in the sunset, 

 and even green. But since the air itself is blue (that is, 

 it lets mostly blue light go through), it is easy to see how 

 this blue can combine with the red or yellow that the 

 dust lets through, to form purple or green. 



But we could not have sunset colors or all the colors 

 we see on earth, if it were not that the sunlight is mostly 

 white that it contains all colors. And that, too, is 

 why we can have a rainbow. 



How rainbows are formed. You already know fairly 

 well how a rainbow is formed, since you made an imita- 

 tion of one with a prism. A rainbow appears in the sky 

 when the sun shines through the rain ; the plain white 

 light of the sun is divided up into red, orange, yellow, 



