what makes a rainbow?
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A rainbow is a prismatic effect, a kind of optical illusion, because of water droplets in the air and the way the sun shines through them.
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When light and water meet in the sky on a summer's day, for a few moments, a rainbow will appear. Such a beautiful sight! This phenomena of the atmosphere appears during or immediately following local showers, when the sun is shining and the air contains raindrops. A rainbow can best be seen with polarized sunglasses. We cannot follow the arc of a rainbow down below the horizon, because we cannot see those droplets in the air below the horizon. But the higher we are above the ground, the more of the rainbow circle we would see. That is why, from an airplane in flight, a rainbow will appear as a complete circle with the shadow of the aitplane in the center.\n\nThe bow is divided into bands displaying the different colors of the spectrum and is formed by the refraction and reflection of the sun's rays in drops of rain. Reflection is simply the return of light waves from the raindrop's surface. Light which appears to be white, is really made up of a mixture of red, orange, yellow, green, blue, and violet light
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Like this?\nhttp://www.webelements.com/webelements/elements/media/pics/rainbow.jpg\n\nTo quote the web site,\n"The picture above shows the result of adding different metal salts to a burning reaction mixture of potassium chlorate and sucrose. The red colour originates from strontium sulphate. The orange/yellow colour originates from sodium chloride. The green colour originates from barium chlorate. The blue colour originates from copper (I) chloride. The lilac colour that should be evident from the potassium chlorate is washed out by the other colours, all of which are more intense."\n\nBasically, certain salts will color the flames various colors due to how the electrons are excited (more complicated than that, look into spectroscopy).
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You can see a rainbow when the light is behind you.  It's reflected by the raindrops.  Light of a particular colour is refected by the raindrops that are at the correct angle between the straight line from the sun to the raindrop and the straight line from the raindrop to your eye.  The raindrops at that angle are in a circle, although of course there aren't any under the ground so you only see an arc.  If you're in a plane and the sun and a raincloud are in the right places, sometimes it's possible to see the whole circle.
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When water falls, it becomes a mist. Then light refraction occurs and the wave length changes. It looks white because it scatters the light. I also creates rainbows because of the light refraction.
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Sunlight is known as white light. Whit light is made up of seven different colored lights: Red, orange, yellow, green, blue, indigo and violet. When a ray of white light passes through a prism, it breaks into its components. This happens because all the seven colored lights have different wavelenghts and slightly diferent travelling speeds. A water droplet acts like a prism and refracts/divides white light into its seven componenets resulting in a rainbow.
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Its the refraction of light, through water droplets. Rainbows can only be seen when the sun is at your back or behind you.
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Sunlight is made up of all the colors of the rainbow: red, orange, yellow, green, blue, and violet. Some of the sunlight is reflected off the surface of the water, reflecting the color of the sky. Some of the sunlight penetrates the water and is scattered by ripples and particles in the water (this tinges the appearance of the ocean with the color of the particles). In deep water, much of the sunlight is scattered by the oxygen in the water, and this scatters more of the blue light.
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A rainbow (also known as a rainboner) is an optical and meteorological phenomenon that causes a nearly continuous spectrum of light to appear in the sky when the sun shines onto falling rain. It is a multicoloured arc with red on the outside and violet on the inside. The full sequence of colours is red, orange, yellow, green, blue and indigo violet. An easy way to remeber the colors is the name Roy G Biv
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Umm.. No. Rainbows are a result of atmospheric moisture and light, not a short Irish man who tricks kids into buying overpriced cereal.
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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.
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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.
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The rainbow is a prism that occurs when light travels through water or something that can bend the light to creat the colors that we call the rainbow.
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As spijk says, the rainbow is formed by the refraction (bending) of light as it passes trhough rain drops. But the reason an observer sees the rainbow as an "arc" is that the sunlight must be refracted at a certain constant critical angle between the arrival of the light ray and the path back to the observers eye for the colors to be seen. This angle occurs over an arc in relation to the observer.  Here's why:\n\n   There are three conditions necessary for the rainbow to be visible:\n\n  First, there has to be water droplets in the air (These   droplets may or may not be falling to the ground as rain), and -\n\nSecond: -  the sun must be behind the observer while looking at the rainbow - and -\n\nThird: - the light rays that become visible as the rainbow must pass through the raindrops at the critical angle.\n\nIf you draw these conditions out in three dimensions, it is apparent that the necessary conditions only prevail to the observer as an arc.  \n\nBy the way, the rainbow is not always a semi-circle! If you're airborne, above the droplets with the sun high in the sky, you will see the rainbow as a circle!\n\nI fly my own plane and have seen this condition on several occasions, and even took a picture of it once!\n\nNow you can understand why seeing rainbows is relatively rare - the conditions for their appearance are not very common, mainly because you have to have water droplets in the air at the same time that the sun is not blocked by clouds!  That's why the most common time to see a rainbow is after a relatively small afternoon thunderstorm cell passes your position (usally passing from west to east), dropping rain beneath it as it passes and then leaving clear sky behind allowing the sun rays to strike the raindrops.\n\nGo to the website below for diagrams on how the rainbow works! A picture is worth a thousand words, especially a picture of a rainbow! :-)\n\neo.ucar.edu/rainbows \n\nBy the way, good question!  You have a keen mind, keep asking questions!  After reading and doing your homework, its the best way to learn!\n\nHope this answer  helps.\n\nCharlieQ
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Rainbows are caused by sunlight reflecting off and refracting through raindrops. There is a very specific angle that each different wavelength of light will take so all parts of the rainbow of that color are always seen at exactly that angle away from the Sun, about 42 degrees for visible light. In math, the collection of all points at a certain distance from a point is a circle, so rainbows are seen as a circle around the sun.
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hmmmm, my bubles have all the colors of the rainbow.\njust need to look closely. a beauty, those colors are slowly flowing over the surface of the bubble, ....then i pop the bubble, muahahahaha.
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Each element has it's own set of "spectral lines" that it gives off or absorbs.  Basically they are lines in a rainbow of color caused by electrons absorbing or giving off specific wavelengths of light.  http://en.wikipedia.org/wiki/Spectral_lines explains it much better then I could.