why are rainbows always in arcs?

Answer 1

What is a rainbow?
Author Donald Ahrens in his text Meteorology Today describes a rainbow as "one of the most spectacular light shows observed on earth". Indeed the traditional rainbow is sunlight spread out into its spectrum of colors and diverted to the eye of the observer by water droplets. The "bow" part of the word describes the fact that the rainbow is a group of nearly circular arcs of color all having a common center.
Where is the sun when you see a rainbow?
This is a good question to start thinking about the physical process that gives rise to a rainbow. Most people have never noticed that the sun is always behind you when you face a rainbow, and that the center of the circular arc of the rainbow is in the direction opposite to that of the sun. The rain, of course, is in the direction of the rainbow.
What makes the bow?
A question like this calls for a proper physical answer. We will discuss the formation of a rainbow by raindrops. It is a problem in optics that was first clearly discussed by Rene Descartes in 1637. An interesting historical account of this is to be found in Carl Boyer's book, The Rainbow From Myth to Mathematics. Descartes simplified the study of the rainbow by reducing it to a study of one water droplet and how it interacts with light falling upon it.
He writes:"Considering that this bow appears not only in the sky, but also in the air near us, whenever there are drops of water illuminated by the sun, as we can see in certain fountains, I readily decided that it arose only from the way in which the rays of light act on these drops and pass from them to our eyes. Further, knowing that the drops are round, as has been formerly proved, and seeing that whether they are larger or smaller, the appearance of the bow is not changed in any way, I had the idea of making a very large one, so that I could examine it better.

Descarte describes how he held up a large sphere in the sunlight and looked at the sunlight reflected in it. He wrote "I found that if the sunlight came, for example, from the part of the sky which is marked AFZ

and my eye was at the point E, when I put the globe in position BCD, its part D appeared all red, and much more brilliant than the rest of it; and that whether I approached it or receded from it, or put it on my right or my left, or even turned it round about my head, provided that the line DE always made an angle of about forty-two degrees with the line EM, which we are to think of as drawn from the center of the sun to the eye, the part D appeared always similarly red; but that as soon as I made this angle DEM even a little larger, the red color disappeared; and if I made the angle a little smaller, the color did not disappear all at once, but divided itself first as if into two parts, less brilliant, and in which I could see yellow, blue, and other colors ... When I examined more particularly, in the globe BCD, what it was which made the part D appear red, I found that it was the rays of the sun which, coming from A to B, bend on entering the water at the point B, and to pass to C, where they are reflected to D, and bending there again as they pass out of the water, proceed to the point ".

This quotation illustrates how the shape of the rainbow is explained. To simplify the analysis, consider the path of a ray of monochromatic light through a single spherical raindrop. Imagine how light is refracted as it enters the raindrop, then how it is reflected by the internal, curved, mirror-like surface of the raindrop, and finally how it is refracted as it emerges from the drop. If we then apply the results for a single raindrop to a whole collection of raindrops in the sky, we can visualize the shape of the bow.

Answer 2

Well if they come up on one side of the horizon they have to make an arc to get to the pot of gold at the opposite end. Seriously, the arc is a parabola made by bending light waves as they strike rain drops or water. I like the double rainbows, one inside the other that cover 1/2 the sky.

Answer 3

G'Day, Mrs.Ahmad,
I am just guessing this one, but I think that it is the curvature of the Earth. O.K. this is my theory, light travels in straight lines and is bent and/or broken into it's colors by a prism. The prism in this case is the Earths atmosphere which is covering the whole of the planet which is a ball. When the part of the atmosphere that you can see is laden with rain drops the light is broken down into it's colors and follow the part of the prism that you can see, hence the arc of color, or rainbow. I hope that make's sense.

Answer 4

The rainbow is actually not an arc... if you look closely it is actually a circle. And isn't there a theory about the pot-at-the-end-of-the-rainbow?

Answer 5

They are part of a circle of points equidistant from the observer. The light from the sun is reflected and refracted by the raindrops and directed to the observer. As all the drops you see in a particular colour must be the same distance from you, the rainbow is circular. You don't see the full circle unless you are in an aeroplane or on a high mountain.

Answer 6

They come out in arcs because god makes them like that, god created everything, if he wants to make them arc shaped, thats how he makes them.

Answer 7

Horizon line is between 0 and 180 degree.

Answer 8

because is always in arcs shape and beautiful.

Answer 9

because there are six telephone books in a bunch of grapes !derrrr!

Answer 10

Because the sun isn't square