Why is a rainbow always arched and why is it in a certain place i.e it could be infront of you or behind?
814724
I know what you mean, you don't want to know why it is changed into the full spectrum due to that the different colours retract better than others but why it does, well i think it is done at random!
424597
Rainbows are caused when sunlight is bent as it passes through raindrops.  Different wavelengths of light (different colors) bend at slightly different angles, which separates the white light into its different colors.  Because there is a specific angle that each color bends, these colors will always be at a specific distance from the sun.  Next time you see a rainbow, you can notice that the sun is either at the center of the rainbow, or else the rainbow is centered at a point directly opposite the sun in the sky.
57096
Rainbows appear to you to be an arc because from where you are standing, only drops within that arc can reflect (or refract) the colored light to your eyes like a prism.  Someone standing a great distance from you would see their very own arc (and a different pot of gold).  Rainbows are kind of special, just for you.  A cloud of smoke is different because everyone sees the same cloud no matter where they are standing, just different views of it.
211510
This site might help "see" what is going on and why.  Interesting question by the way.  I saw my first one last summer and the colors were so bright.  It was amazing!  Had everyone out in the parking lot of the strip mall checking it out.\n\n\nhttp://hyperphysics.phy-astr.gsu.edu/Hbase/atmos/rbowpri.html\n\nhttp://en.wikipedia.org/wiki/Rainbow
773813
Rainbows don't exist.  What you can see is the light from the sun (behind you) relected and refracted by raindrops.  You can't go there - what you see would move with you.\n\nYou can only see a rainbow where there are raindrops.  It seems to end where it touches the ground, but that's because there aren't any raindrops down there.  If you could get high enough, you would be able to see the whole circle - so there's no end.
30370
There are different colors of light that make up white light. Each color bends by a different amount when it enters a slow medium, like the glass of a prism or the water of a rain drop. Red bends the least, and violet bends the most. When the different colors bend from passing through a slow medium, they get separated, as in a rainbow. \n\nBy the way, if you see a rainbow from an airplane, it will not be an arc, but can be a complete circle. \n\nAlso, sometimes you can see a 2nd fainter rainbow next to the first, with the colors in the opposite order. \n\nIn the laboratory, it is possible to see a 3rd rainbow, fainter still, and even 4th, 5th,...and even 12th rainbows from a single drop of water, and as many as 19 rainbows from a stream of water! \n\nThere are also even more interesting "supernumerary" rainbows with other color orders that appear just under the main rainbow or sometimes the secondary rainbow, that you might have observed sometimes. Look at the pictures in the references I found.
968711
A rainbow is curved due to angle requirements.  Light from the sun that\nbounces through a drop of water, comes into your eye, and appears red must\nbounce at a specific angle.  Join two sticks together at a set angle.  Place\none end at a dot to represent the sun.  Place the other toward your eye.\nThe place where the sticks join, where the water drop is, can be rotated\naround in a circle.  A rainbow is shaped like a circle.\nWell,\n\nYou never see the entire rainbow because of the horizon.  When you look at a\nrainbow, the Earth gets in the way of most of the circle.  The portion you\nsee is just the top portion.  Draw a circle and cover a little more than\nhalf of it.  What is left is the shape of a rainbow.\n\n____________________________________________________\nWhy 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. \nConsider 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.\n\nAlso 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.\nIt 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.
285200
if there is, it moves around when you do. If you try nd follow the rainbow till its end, you will never manage it, as much as you try. So there might be, but you'll never get it.
1164808
Each drop bends the light by the same angle to make one small spot in the rainbow. It is the combined light from millions of drops at different places that makes up the arc of the bow. The arc is simply the collection of places where the angle from the sun to the drop to your eye is equal to the angle at which light in one drop bends. Different colors bend by slightly different angles. Red light bends a little more than blue light, so all the red spots form an arc a little farther from the Sun and the blue spots form an arc a little closer to the sun.
465572
because the bands of color that appears when the Sun's rays are refracted and reflected by drops of mist or rain. The colors of the rainbow are conventionally said to be red, orange, yellow, green, blue, indigo, and violet.\nIn shorter words the drops of water work like a prism that when are touched by the sun'srays thansform light into many colors that then form many bands called rainbow.
416298
A full moon can form a rainbow - usually called a "moonbow". It looks kind of grey though.
172613
We can see two simultaneously rainbows sometimes. The first one is produced by one internal reflection inside the raindrop, and the second one is produced by two internal reflections.\nTheorically, light can reflect more times inside the raindrop, but I think nobody has seen a third rainbow.
961441
Rainbows are always the same size.  The diameter of a rainbow is best expressed in degrees as it is not at a fixed distance away.  Rainbows can be thought of as occupying the surface of a thin cone with its pointy end at your eye, and the angle of the cone is fixed.  This angle depends only on the refractive index of water.\n\nYes - you can get one bigger than a semi-circle, but only if you get well above the earth's surface (perhaps in an aeroplane) so that the ground doesn't get in the way!
942352
A rainbow is an optical and meteorological phenomenon that causes a nearly continuous spectrum of light to appear in the sky when the Sun shines onto droplets of moisture in the Earth's atmosphere. It takes the form of a multicoloured arc, with red on the outside and violet on the inside. A double rainbow includes a second, fainter, arc with colors in the opposite order.\n\nEven though a rainbow spans a continuous spectrum of colours, traditionally the full sequence of colours is most commonly cited as red, orange, yellow, green, blue, indigo and violet. It is commonly thought that indigo was included due to the different religious connotations of the numbers six and seven at the time of Isaac Newton's work on light, despite its lack of scientific significance and the poor ability of humans to distinguish colours in the blue portion of the visual spectrum.\n\nScientific explanation\n\nThe rainbow effect can be observed whenever there are water drops in the air and sunlight shining from behind the observer at a low altitude or angle. The most spectacular rainbow displays when half of the sky is still dark with draining clouds and the observer is at a spot with clear sky overhead. The rainbow effect is also commonly seen near waterfalls or fountains. Rainbow fringes can sometimes be seen at the edges of backlit clouds and as vertical bands in distant rain or virga. The effect can also be artificially created by dispersing water droplets into the air during a sunny day.\n\nIn a very few cases, a moonbow, or night-time rainbow, can be seen on strongly moonlit nights. As human visual perception for colour in low light is poor, moonbows are most often perceived to be white.\nRainbows may also appear in the spray of a water fountain\nEnlarge\nRainbows may also appear in the spray of a water fountain\n\nThe rainbow's appearance is caused by dispersion of sunlight as it is refracted by (approximately spherical) raindrops. The light is first refracted as it enters the surface of the raindrop, reflected off the back of the drop, and again refracted as it leaves the drop. The overall effect is that the incoming light is reflected back over a wide range of angles, with the most intense light at an angle of about 40°–42°. This angle is independent of the size of the drop, but does depend on its refractive index. As seawater has a higher refractive index than rain water, the radius of a 'rain'bow in a sea spray is smaller than a true rainbow. This is visible to the naked eye by a misalignment of these bows [1].\n\nSince the water is dispersive, the amount that the sunlight is bent depends upon the wavelength, and hence colour, of the light's constituent parts. Blue light is refracted at a greater angle than red light, but because the area of the back of the droplet has a focal point inside the droplet, the spectrum crosses itself, and therefore the red light appears higher in the sky, and forms the outer colour of the rainbow. Contrary to popular belief, the light at the back of the raindrop does not undergo total internal reflection; however, light that emerges from the back of the raindrop does not create a rainbow between the observer and the Sun. The spectra emitted from the back of the raindrop do not have a maximum of intensity, as the other visible rainbows do, and thus the colours blend together and do not form a rainbow.\n\nA rainbow does not actually exist at a location in the sky, but rather is an optical phenomenon whose apparent position depends on the observer's location. All raindrops refract and reflect the sunlight in the same way, but only the light from some raindrops reaches the observer's eye. These raindrops are perceived to constitute the rainbow by that observer. The position of a rainbow in the sky is always in the opposite direction of the Sun with respect to the observer, and the interior is always slightly brighter than the exterior. The bow is centred on the shadow of the obser
775696
An inverse rainbow is when the colors are reversed so that the red band of color is on the inside of the rainbow and the blue band is on the outside.  Moonbows, or, halos, are inversed. I wasn't aware that rainbows were different here and there. If they are, my guess is the explanation would be found in optics and, maybe bioelectric fields stuff? Here's a GREAT website for future reference and to put in your Favorites file.  Just click on any "circle" of science and follow the algorithm. Handy little tool. Can't wait to come back and read if someone has an explanation.\nhttp://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
436348
A rainbow is seen when the Sun is behind you and water is in the air in front of you. You can make one with a water hose or maybe see one in the air with rain in the area. Natural rainbows appear very large and several miles away. The top is all you can see because the ground in front of you blocks the lower portion of the rainbow. However, when seen from an airplane, rainbows are complete circles.
62795
Actually, all rainbows are complete circles, we just can't see the bottom half due to the horizon.\nIf we were high enough, we'd be able to see the rainbow, loop around the bottom.