I saw a halo of rainbow around the sun around noon,  what caused this?
545051
The sundog is caused by the same thing that a rainbow is caused by- refraction of the sun's light through water particles (most likely frozen, so ice particles) around the area of the sun.\n\nVisible white light is actually all of the colors of light rolled into one.  So, when a light beam encounters a droplet of water/ice particle, it can have a prism effect and split into all colors of the visible spectrum.\n\nThis could be caused by a group of cirrus clouds in front of the sun, which is the most common.
7285
THe bright ring is called a 'halo'\n\nIt's a fairly common sight and occurs when high thin clouds containing millions of tiny ice crystals cover much of the sky. Each ice crystal acts like a miniature lens. Because most of the crystals have a similar elongated hexagonal shape, light entering one crystal face and exiting through the opposing face refracts 22 degrees, which corresponds to the radius of the Moon Halo. \n\nSee a nice picture here:\nhttp://antwrp.gsfc.nasa.gov/apod/ap000515.html
64520
Its the refraction of light, through water droplets. Rainbows can only be seen when the sun is at your back or behind you.
122346
Why don't you search the answers to the previously posted questions here on this topic? This has been asked over and over. \n\nHere is a little bit to get you started:\n\nRainbows are caused because the different colors in white light are bent by different amounts in rain drops, so the colors get separated. The sun shines from behind the observer, and then bounces off the back surface of the raindrops, and those raindrops that are at the required position for light to reach the observer from the sun contribute to the rainbow. This arc is formed by the collection of raindrops which are at the vertices of angles of 42 degrees between the observer and the sun.
416298
A full moon can form a rainbow - usually called a "moonbow". It looks kind of grey though.
357161
Was the object moving extremely fast? If so, it was almost certainly a meteor. The changing colors could have resulted from different chemical elements being burned off.\n\nIf it was moving steadily, then it could have been an artificial satellite. I'd say it was in a very high orbit too because sunlight was still reflecting from it although where you were was in complete darkness. The color changes could have been caused by the reflected light passing through atmospheric layers of varying density and composition.\n\nGod should be spelled B-I-G B-A-N-G\nPBrax@netscape.com
780823
Could be a strange mirage. Sometimes weird mirage can project skyline of cities beyond horizon or just strange shapes in sky when atmosphere refract lights in unusual ways.
483599
the other answers are somewhat correct but unnecessarily long....\n\n1. the rainbow is actually a circle that is partially visible as an arch due     \n    horizon limitations.\n\n2.  it is a circle because the light source ( the sun ) is a circle.
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.
661394
it occurs when solar radiation from the sun interacts with the magnetic field around the Earth (its strongest around the poles..so thats why theres a northern..AND southern lights...and no "Middle" lights lol)\n\ni can't wait to see it some day
52478
When light is refracted off of droplets of water it enables you to see all the colors that make up white light (sunlight, even light from bulbs.) creating what people more commonly refer to as a rainbow. \n  Go outside on a sunny day and spray the waterhose if you have one. If you look very carefully, you can see that the rainbow you created is not just a semi-circle, but a full circle! The bottom half is harder to see, but it is there. The reason rainbows don't look like that when we see them outside is because we are too low to the ground to see the rest.
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Although sightings of these colorful events have been documented in the past, this phenomena has come to the front of geophysical interest in recent times. Red sprites typically extend above the cloud tops up to heights of nearly 95 km. After several imaging campaigns in the central United States during1993 and 1994, there has been an increased demand to explain these naturally-occurring colorful flashes. The VLF group is actively pursuing scientific explanations along with our colleagues in the field. \n\nmore info in\nhttp://www-star.stanford.edu/~vlf/Red_Sprite/
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You must realize that this has been asked over 500 times here. Surely when you asked this question you were notified. Why didn't you look at some of those previous questions and answers? I probably have answered this 50 times myself. I have some very careful detailed answers here to that question, if you just look. \n\nIt is called Rayleigh-Tyndall scattering, caused by the small size of the nitrogen and oxygen molecules in the air that scatter the blue out of the sunlight, leaving it more yellowish than it would be otherwise. At sunset, the reddish color is absorbed by the ozone overhead, creating a deep blue. \n\nIf you want more details, look it up.
294562
I saw a lovely sunset, with a triple (yes, triple!) rainbow in West Texas, USA a few years back.
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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.
143433
Prismatic refraction through water vapors in the atmosphere.\n\nAs light shines through the atmosphere, certain things like temperature, barometric pressure, and humidity (the amount of water vapor in the air) come together to produce the right conditions for prismatic refraction.  This is the same process by which rainbows are produced, but can also produce halos around the sun or moon.
765835
Wow, not enough information to calculate. We would need the following information:\n\nYour position in latitude and longitude\nTime of day to the minute\nThe position of the clouds that are raining\n\nThen, let's state a few facts...\n\n1) Rainbows do not have a position, they are an optical illusion. The refraction/reflection can be inches away or thousands of feet. You would not necessarily know the distance by looking.\n\n2) You can only see a rainbow when the light source is behind you.\n\n3) There is no base of a rainbow because they do not exist, remember they are an optical illusion. You can see where the rainbow appears to be cut off by the ground, but there is no base. In fact if you were in the right position you could see a full circle rainbow.\n\n4) There is no location to move on a rainbow, but if you did move, yes it would look like the rainbow moved too. In fact there is no way to could be in a rainbow. HOWEVER, that does not mean a friend could not move to a position and appear to be in the rainbow, however your friend would not see the rainbow.\n\n5) Seeing dual rainbows (one at 42 degrees and the next at 50 degrees) is not uncommon. Seeing a triple or quadruple is much more unusual.\n\nSO there you go, so rainbow facts.