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# Why does a rainbow appear bent or arched in a semicircle in the sky?

Wiki User

2009-04-26 15:26:49

Rainbows have been the subject of songs and poems, stories and mythology, but there is an explanation as to why rainbows appear as they do. Rainbows are light and you can't touch them. The sun must be shining and must be behind you, and there must be water droplets in the air in front of you. Sunlight shines into the water drops which act as tiny prisms that bend or "refract" the light and separate it into colors. Rays of a rainbow bend twice. As they enter the drops, the rays are bent, then they reflect off the back of the drops and bend again as they exit out the front of the drops. The rainbow is circular because when a raindrop bends light, the light exits the raindrop at a 40-42 degree angle away from the angle it entered the raindrop. The violets and blues bend at a 40 degree angle, and the Oranges and reds bend at a 42 degree angle. Light can also enter droplet, be reflected off the back of the droplet, only to be reflected of the front, and then off the back again before leaving. It is bent at each phase in this process, and a second rainbow can appear above the first one. In a double rainbow, the second rainbow will appear where it does because the light will be cumulatively bent some 50 to 53 degrees. This gives it its position "outside" the primary rainbow. Also, the colors will be inverted in this bow. Rainbows don't have "ends" but are full circled, but we can't see this because the horizon of the earth is in the way. If the sun is very low in the sky, either just before sunset or just after sunrise, we can see a half circle. The higher the sun is in the sky, the less we see of the rainbow. The only way to see the full circle of a rainbow in the sky is to be above the ground and have the sun behind you. You would have to look out on the drops from an airplane to see a circular rainbow. Now, this is quite complex, so it's possible you might get away with the old standard, "There is gold at the end of the rainbow and that's what makes the colors." Be sure that you watch your 6-year old closely as he/she might decide to pack his/her bags and go hunting for that bag of gold! Another way you may get away with explaining this off is buying a "prism" (it's a glass drop) and hanging it in a sunny window. It will reflect beautiful spots of light in the room and the effects are quite pleasant to study. Another way to view a full rainbow without leaving the ground is using a garden hose. Have it spray water in bright sunlight with the sun behind you and the spray in front of you. If the entire circle is not visible you can move the hose around to see the rest of the circle. The ones seen from airplanes are more spectacular, though.

Wiki User

2009-04-26 15:26:49
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