why are rainbows in the shape of an arch?  why not a flat sheet of rainbow colors?
919329
Because of the Earth's atmosphere and the moisture in it's ability to bend light.
270700
much to many people's belief's 7 basic colors aren't based on the rainbow colors. in fact some of the colors on the rainbow is actually a mix of primary colors that are really secondary or tetiary. not primary [basic]. so... here we go...\n\n\n7 basic colors are:\n\n1- a cool yellow a.k.a Hansa Yellow Medium—a lemony, slight bias to blue-green;\n\n2- a warm yellow a.k.a New Gamboge— a golden, slight bias to red-orange;\n\n3- a cool blue a.k.a Phthalo Blue (GS)—an icy, slight bias to blue-green;\n\n4- a warm blue a.k.a French Ultramarine— a purplish blue, slight bias to violet;\n\n5-  a cool red a.k.a Quinacridone Rose—a rosy, slight bias to red-violet;\n\n6- a warm red a.k.a Pyrrol Orange—a tomatoey red, slight bias to red-orange;\n\nok..only six [6] are listed here. to get the 7th color,all u need to do is... well here's where the magic is....\n\na] Use a warm and a cool of each primary hue (a warm red and a cool red; a warm yellow and a cool yellow; a warm blue and a cool blue) to mix bright, high-inten sity secondary called a Mixed Primary Hue. The secret is in using the right split primary colors and not crossing over the lines into another section!\n\n++TIPS++\n\nTo mix the oranges, mix the red and yellow within the lines to the left of the circle. First mix orange, and then add more yellow for yellow-or ange and more red for red-orange. \nTo mix the greens, mix the blue and yellow within the lines to the right of the circle. First mix green, and then add more yellow for yellow-green and more blue for blue-green. \nTo mix the purples or violets, mix the pink or rose with the blue within the lines at the bottom of the circle. First mix purple , and then add more blue for blue-violet and red for red-violet. \n\nNow here's the rule that makes this work: 'When mixing two colors on the wheel to achieve high- intensity color, don't cross over the line-stay in each section. Just imagine, no more muddy colors!\n\nCrossing over the lines and mixing the colors on either side of the line causes the mixtures to become less intense and slightly grayer. Cross two lines and even more graying occurs. This graying is called neutralizing. It is the result of a slight touch of that third color being added to the mix. To mix earth colors, you simply cross over the lines or add a warm neutral to your mixtures.\n\nOK ...\n\nNow for the much awaited 7th basic color....\n\nThat's where Quinacridone Burnt Orange—the seventh color of our essential 7 basics-enters the scene… it's a versatile warm neutral.\n\n\nhehe. quite interesting. hmm. [^_^]
1173045
You know how you see a rainbow when its really humid, or when it rains and there is sun? Thats what you saw, you saw a rainbow, but not a half rainbow, but rather a whole rainbow around the sun. A ring rainbow, this is due because of the high humidity that is in the air, its the same as a rainbow, just around the sun.
328568
Not sure, but I like rainbows and can't wear them anymore without people thinking I'm gay. I guess it's just a symbol of happiness and positivity.
265331
The only reason color exists is because objects (rain drops in this case) reflect certain wavelengths and obsorb certain wavelengths of light.  The only reason we see the colors in the rainbows is because the sun produces white light which, when refracted, will produce ALL OF THE POSSIBLE COLORS.  This is interesting, you will notice there is no brown in the spectrum (or rainbow); therefore, brown is not a color.  The sun doesn't have the same color as the rainbow, the rainbow has the same color as the sun.
246417
Because the physics are: the sun at a 42 degree angle, behind you, and the fact the watger droplets in the air make the rainbow, and the world and consequently the air is curved.
529953
It has to do with the angles of refraction.  Rainbows are formed when you have the sun behind you and the sun is hitting a group of water droplets in the direction of the rainbow.\n\nThe light from the sun hits a droplet, bounces around and comes back out toward you at an angle of around 42 degrees (technically between 40 and 42 depending on the color).  In fact it is hitting lots of droplets and rays are bouncing in all sorts of directions, but only the ones that bounce toward *your* eyes are the ones you see.  It turns out that you see all drops that are 42 degrees from your viewing point.  That would be 42 degrees up, 42 degrees left, 42 degrees right, 42 degrees up and left, etc.  If you think about connecting all those points, it forms an arc, not a straight line.  An illustration is included in the 1st link below.\n\nIf you are in an airplane, you can actually see a full circle but because we are usually on the ground, you can't see the bottom of the circle.  Tale a look at the 2nd link.\n\nFinally, if you look closely at a rainbow in a sprinkler, you *will* notice an arc.  It may be a much smaller portion of the circle (since you have a small sprinkler compared to a large bank of rain droplets), but you should see the bend.  And example is in the 3rd image link.\n\nAnyway, the arc of a rainbow has nothing to do with curvature of the earth or a "cylinder" of light.  It's all in the angle of refraction in the light rays.
380553
When we draw a circle with a compass, we keep the angle between the two legs constant.\n\nA ray from the top most point on the rainbow to our eye makes an angle to the horizontal direction. Theory says this angle is a constant.\n\nImagine the ray as one leg of long compass and the horizontal direction as another leg which points the center. Keeping the angle constant when the compass is rotated an arc is formed. \n\nIf we go high up we can see the whole circle.
445187
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.
1052262
erm... rainbow forms when the sun shows up after a rain. this is because after a rain, the air is very humid, which means got water particles. when sunlight passes through these water particles, they are split into 7 colours, because of refraction. different colours means the colours travel in different speed. the red is the fastest, while the purple is the slowest. if the 7 colours are combined together, they will form the white, or transparent, light again. keep in mind that the rainbow only forms at the opposite of the sun.
787816
Black, White are not in the rainbow either\n\nA rainbow is white light seen through a prism (the prism being\nthe raindrops).  The prism breaks the light into all the colors that make up white - so you do not see white because white is a combination of colors.\nBlack is an absence of light, so it is not in the rainbow.  Brown is a combination of rainbow colors, so you do not see it in the rainbow.
379722
The 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.\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 perceived to be white.\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°, regardless of the size of the drop. Since the water of the raindrops 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 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 observer's head, or more exactly at the antisolar point (which is below the horizon during the daytime), appearing at an angle of approximately 40°–42° to the line between the observer's head and its shadow. As a result, if the Sun is higher than 42°, then the rainbow is below the horizon and cannot be seen unless the observer is at the top of a mountain or a similar vantage point. Similarly, it is difficult to photograph the complete arc of a rainbow, which would require an angle of view of 84°. For a 35 mm camera, a lens with a focal length of 19 mm or less would be required, whilst most photographers are only likely to have a 28 mm wide-angle lens.\nFrom an aeroplane, one has the opportunity to see the whole circle of the rainbow, with the plane's shadow in the centre. This phenomenon can be confused with the glory, but a glory is usually much smaller, covering only 5°–20°, as opposed to over 80° for a full circle rainbow.
547532
Your nearest rainbow? Just kidding!\nTry this site: http://physics.nist.gov/PhysRefData/Elements/legend.html
962067
The main colors of a rainbow are red, orange, yellow, green, blue, and purple, but there isnt usually that much purple. By the way, that list is from outside to inside.
388125
A rainbow occurs when sunlight passes through sheets of falling rain which act as a prism to separate the light into it's full spectrum of colors. A double rainbow occurs when there are multiple sheets of rain that are perhaps angled slightly differently. One sheet of rain bends the light into one rainbow, the other sheet of rain bends the light in a slightly different path to create a second prismatic display. \n\nBasically, it is like haveing one light source (the sun) and two separate prisms set next to each other, but at slightly different angle giving you two separate spectra or rainbows.\n\nDouble rainbows are very cool indeed. I saw one last summer!
1103987
Rainbows are 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, reflects off the back of the drop, and is 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°, regardless of the size of the drop. Since the water of the raindrops is dispersive, the amount that the sunlight is bent depends upon the wavelength (color) 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 spectra crosses itself, and thus the red light appears higher in the sky, and forms the outer color of the rainbow.\n\nA rainbow 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. Its position is always in the opposite direction of the sun with respect to the observer, and the interior is actually a magnified image of the sun, which can be seen to be slightly brighter than the exterior. The bow is centred on the shadow of the observer's head, or more exactly at the antisolar point (which is below the horizon during the daytime), appearing at an angle of approximately 40°–42° to the line between the observer's head and its shadow (this means that if the sun is higher than 42° the rainbow is below the horizon and cannot be seen unless the observer is at the top of a mountain or a similar vantage point).\n\nSometimes, a second, dimmer rainbow is seen outside the primary bow, caused by a double reflection of the sunlight inside the raindrops, and appears at an angle of 50°–53°. Because of the extra reflection, the colours of the bow are inverted compared to the primary bow, with blue on the outside and red on the inside. (The full sequence of colors is red, orange, yellow, green, cyan, blue and violet.)\n\nA triple rainbow is even more rarely seen. A few observers have reported seeing quadruple rainbows in which a dim outermost arc had a rippling and pulsating appearance.
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When we draw a circle with a compass, we keep the angle between the two legs constant.\n\nA  ray from the  top most point on the rainbow  to our eye makes an angle to the horizotal direction. Theory says this angle is a constant.\n\nImagine the ray as one leg of long compass and the horizontal direction as another leg which points the center.Keeping the angle constant when the compass is rotated an arc is formed.   \n\n Mathematically we say that the locus of all such points is an arc of a circle.\n\nIf water particle were present on all points on the arc we see a continuous arc of a rain bow.\n\nDuring cloudy  night we can see a full circle of rainbow \naround moon with moon as center.