why rainbow has that kind of arc form? why not triangle?

Question

I know why rainbow has seven colours ,

bit why it has that form?

Answer 1

http://en.wikipedia.org/wiki/Rainbow#Scientific_explanation
Shape of water droplets - Relative position of observer+sunlight+droplets - sunlight nature - refractive index of water

Answer 2

Actually, the shape of a rainbow has NOTHING to do with the shape of the earth's surface. If you are facing a region filled with spherical droplets, and you have a relatively point-like light source behind you, a portion of the light will be refracted inside the droplets and then reflected from an interior surface back at some angle which is not always 180 degrees. The light which comes to your eyes from all of this falls within a small angular range. The exact angle is dependent on the amount the light is refracted, with shorter wave lengths being refracted less than longer ones, thus the color separation effect. There is in effect a cone of light which has been refracted/reflected which would be refracted so that it comes to your eye, so the return of the rainbow is a circle. Part of this circle is occluded by the ground, so you see an arc. When flying above a mist, with the sun overhead, you can see the full circle. If you were out in space, facing a mist with one star behind you, and no planet anywhere nearby, you would see the circle. The shape of the body upon which you stand is inconsequential.

Answer 3

Actually, a rainbow would appear as a complete circle if it was high enough. Why? Because droplets of water acting like prisms are everywhere, and you more or less have to be at the summit of a cone with the rainbow being the base. The light from the side has to come from the proper angle to you to disperse the colour in the right way, and since all points having this property of equivalent angle do form a circle, that is why a rainbow will be circular.

By the way, a rainbow does not have 7 colours, it has an infinite numbers (like yellowish orange, orangy yellow, etc) since this is a continuous spectrum going from the deepest red to the highest frequency violet. Saying 7 colours is just an usual classification.

Answer 4

Vinnie gives you the right answer. Rainbows are reflected, you will only see them with the sun behind you. Also you only see the colours if you are at the correct angle to the reflected light which is why you see the bands of colour instead of colour everywhere. And as he says, you would see a complete circle if you were above the clouds looking down like a pilot in a plane, but on earth the ground cuts off the bottom of the circle. the higher up a mountain you go the more complete the rainbow is. please give him the best answer because he deserves it.

Answer 5

It has to do with the shape of the raindrop and the colors the white light from the sun is refracted into. Blue light is refracted the most as it enters and leaves the raindrop and red light is refracted the least. This spreads out the colors. Then, blue light has a shorter wavelength so it bends in a tighter circle and therefore is at the bottom of the rainbow. The opposite is true of red which has the longest wavelenth and therefore bends the least and is on the top of the rainbow.

Answer 6

It is probable because the Earth and Sun are round. The rays of light from the sun are in all direction or spherical. When i shone onto the water particle it forms an arc shape.

Answer 7

When you see a rainbow you're looking at refracted sun's light rays hence you see the curve of the earth and the colors of white light (the rainbows colors). White contains all colors!

Answer 8

Because sun and earth both are sphere in shape.Light passing and getting objects are of curve edges.This is the reason for the arc form.

Answer 9

because it obeys the shape of the earth surface.