why rainbow is circular , why it is not triangular something else?
962965
Here's what happens: imagine you're standing with the Sun at your back looking at a water drop. As a light ray from the Sun hits the drop, it is bent inwards, toward the center of the drop. It bounces off the back of the drop (coming towards you again) and then refracts again on its way out. As a result you see the light ray appearing to come from some point behind the drop, that is, on the opposite side of the sky from the sun (which is where you see rainbows!) \n\n\nBut what about the colors? It turns out that each color of light is bent a little bit differently - red light is bent the least and violet the most. So, each color appears to be coming from a slightly different place behind the water drop. \n\nThe rainbow is circular because only drops located at certain places on the sky (in a circle around the point opposite the Sun) redirect the light exactly back toward your eye. It's only the light from those drops that you see, and hence you see a circle.\n\nanother explaination: This is difficult to envision and to describe, but we'll use some real common sense objects for our model. Picture yourslf standing in front of a tunnel, like you might find under a bridge - a nice even, round, smooth tunnel. Now, if you cast a shadow parallel to the ground, like a shadow from a power line (not the pole, the line - which is parallel to the ground) and let the shadow fall inside the tunnel, you can imagine that the shape of the shadow on the ceiling of the curved tunnel looks as though it is arced, even though the source of the shadow is a straight line. Can you picture that? This is what is happening in the atmosphere. The rainbow is actually a straight line, since light travels in a straight line. Its just that the straight line is falling across a 'fish bowl' like pocket of moist, reflective air, like our tunnel in the model. The rainbow appears, therefore, to be an arc.
566742
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
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.
655891
It doesn't matter if the rainbow appears around the sun or on the ground after a rainshower. The two rainbows are called primary and secondary bows. There are two because the sunlight is relected off the inside of a water droplet twice instead of once; once would result in only one rainbow. This all depends on the angle in which the sunlight enters the water droplet.\nThe secondary bow is fainter and  the colors are reversed.
506644
1. Its impossible for a circluar shape to fall in. If it was a square, it could have easliy fallen in.\n\n2. Its easier to roll a circular cover to the hole, rather than carry a sqauare cover on a wheelbarrow.\n\n3. Its so easy to fit a circular cover to the hole, whereas a square one will have to be turned to the correct alignment to fit. (Sorry for the 3rd. LOL).
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.
715473
A rainbow is formed when sunlight passes through water droplets.  The light is bent allowing the entire color spectrum to be visible.  The color spectrum is always present, but not always visible to the naked eye.  A prism also produces the same effect as it also bends the light allowing the color spectrum to be visible  This is also why the sky is blue.  The light is bent as it passes through the atmosphere and allowing the color blue to be visible to the naked eye.  This process is know as refraction.
393409
They don't have dark sides, because rainbows are light by their own nature, but they do have a "hidden half"; rainbows are actually giant circles that have their bottom half obscured by the horizon.
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.
507580
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. Even 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\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 perceived to be white.\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°, 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\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 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 vie
547532
Your nearest rainbow? Just kidding!\nTry this site: http://physics.nist.gov/PhysRefData/Elements/legend.html
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.
243764
im a geo student, but i havent done proofs for a long time sorry. ok\n2. false, because squares are parallelograms with 4 congruent sides and 4 right angles, while kites have 2 pairs of congruent sides and only 1 pair of congruent angles that are NOT right angles\n3. false, because a rhombus is a parallelogram with 4 congruent sides, while a kite is any thing BUT a parallelogram. enuff said\n4. false, because kites are quadrilaterals with only two pairs of congruent sides, while the quadrilateral mentioned has 3 congruent sides\n5. false, for example- do trapezoids have 4 congruent sides, and 4 right angles, and is a parallelogram (characteristic of squares)? i think NOT\n6. read above- trapezoids are not parallelograms.
613272
could be circle because it doesn't have any sides or angles\n\ncould be rectangle because it is not proportional (side-wise.. and only if the triangle is equilateral)\n\ncould be triangle because if all shapes are placed right-side and divided into four equal parts, like a cross-hair, the triangle is the only one without equal portions.
160214
They also occur as a circle, if you're in a plane (i was in a microlight) above mist/cloud it's the most spectacular sight, I looked down and there was a circular rainbow. It has to do with the fact that you're viewing it from one point, all the rainbow is relative to you.
416298
A full moon can form a rainbow - usually called a "moonbow". It looks kind of grey though.
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.