why is rainbow in that shape but not a straight line?

Answer 1

A rainbow is curved due to angle requirements. Light from the sun that
bounces through a drop of water, comes into your eye, and appears red must
bounce at a specific angle. Join two sticks together at a set angle. Place
one end at a dot to represent the sun. Place the other toward your eye.
The place where the sticks join, where the water drop is, can be rotated
around in a circle. A rainbow is shaped like a circle.
Well,

You never see the entire rainbow because of the horizon. When you look at a
rainbow, the Earth gets in the way of most of the circle. The portion you
see is just the top portion. Draw a circle and cover a little more than
half of it. What is left is the shape of a rainbow.

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Why does the light that is dispersed by the rainbow forms a bow? The answer involves the use of some simple geometry. The first point is that a rainbow is not a two-dimensional arc; it is in fact a three dimensional cone with the apex at the observer's eye. The reason that it appears to be only a two dimensional flat object isbecause there is no evidence of distance. All the drops, which disperse lighttowards the observer to form the rainbow, lie in the shape of a cone withmany different layers. The outside layers disperse the red component, thelayer below that - the orange component, and the layer below that -the yellow component, etc.
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 in the sky, we can visualize the shape of the bow.

Also consider only the dispersion of the red component of the light. It has been shown previously that the red component is seen when the angle between the incident rays and dispersed rays make an angle of 42 degrees. Of course beams are dispersed at 42 degrees from drops all over the sky in all directions up, down, left, and right. However, only red light, which reached the observer eye, comes from the water drops which are on the cone with sideto axis angle of 42 degrees. If the observer's eye is at the apex of the coneas shown in Figure 3, then to see the violet part of the bow we would needto look at 40 degree to the conical axis. Therefore, the cone that producesthe violet component comes from a cone inside that of the cone which producedthe red part. The same argument can be made for all the other colors, andbecause different colors are formed by different cones, when they are viewedfrom the apex they appear in the form of a bow.
It is interesting to note that because only the drops on the cone with apex at the observer's eye are responsible for the formation of the rainbow, which an observers sees, then an important implication is that each person looking at a different rainbow. That leads to another interesting fact that both of the observer's eyes actually see a different rainbow, as they are both at the apex of different cones.

Answer 2

1. The rainbow is not actually semi sphere
2. It is Round, we can clearly see this form an air-plane.
3. We can't see all colours in a rainbow because of their wave lengths. Mostly we see red, yellow, purple/indigo and white.
4. The rainbows are formed only in direction opposite to the sun.
5. Not all clouds make rainbow and every time it rains won't form a rainbow.

Hope my answer has cleared your doubts.

Answer 3

due to surface tension its tendency is to make smallest surface area so it is spherical
rainbow comes from the reflection of the sun on the vapour in the sky. sun is round shape so is the rainbow

Answer 4

rainbow comes from the reflection of the sun on the vapour in the sky. sun is round shape so is the rainbow.

Answer 5

IT'S THE SHAPE OF THE EARTH!!!!!!!
RAINBOWS WOULD LOOK HORRIBLE IN A STRAIGHT LINE!!!!!!

Answer 6

no longer all diffraction happening in nature ensue in the form of Rainbows. I even have taken some photos of at cutting-edge "Rainbows" that are in actuality very at cutting-edge which we observed while driving over Colorado.

Answer 7

nothing in nature is in a straight line.

Answer 8

b coz our earth is globe shaped