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

Rainbows

Rainbows have been the subject of songs and poems, stories and mythology, but this is 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 drops 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 light bent, then reflect off the back of the drops and bend again as they exit the drops.

Each drop reflects only one color of light so you can imagine how many drops there must be when you get colors of gold/violet/pink, etc.

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.

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 the rainbow.

The only way to see the full circle of a rainbow in the sky is to be above the raindrops and have the sun behind you. You would have to look down on the drops from an airplane.

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 and he/she doesn't decide to pack his/her bags and go hunting for that bag of gold! He, he, he.

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 is quite pleasant to study.

More input:

• 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.

• About previous answer - the Earth's curvature has nothing to do with this.

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First answer by Marcy. Last edit by ID2606644957. Question popularity: 76 [recommend question]