Origin of the Rainbow

英语作文
作文地带题目：Origin of the Rainbow
文章细节：作文地带整理 标题：Origin of the Rainbow
Rainbow (Rainbow) is a meteorological phenomenon in an optical. Sunlight into the air when the rain, light by refraction and reflection, in the sky to form the colorful arch of the spectrum. Colorful rainbow colors, from the outside to inside are as follows: red, orange, yellow, green, blue, blue and purple. 　
Rainbow is because the air close to the sun reach the small round droplets, resulting from dispersion and reflection. When the sun drops into a different perspective of the incident at the same time, in the water droplets with different perspectives is also reflective. Among 40-42 degrees to the strongest reflection, resulting in the rainbow we see. This reflection, the sun drops into the first refraction first, and then drop the back reflection, the final refraction when leaving a water droplet. Because the water dispersion of light there is the role of the different wavelengths of light have different refractive index, Blu-ray refraction angle than red light large. As a result of light reflection in the water droplets have been, so the observer 　
See the spectrum is reversed, red in the top of the other colors the next. 　
In fact, as long as there is air in water droplets, and the sun is low behind the observer's point of exposure, they may have observed the phenomenon of the rainbow. Rainbow the most common in the afternoon, after the rain just fine when transferred. At this time the air is full of dust and small droplets less, because one side of the sky and rain clouds are still dark. The observer is no longer the head or behind the clouds block the sun and can be seen, this rainbow will be seen more easily. Another place to see the Rainbow Falls is near. In fine weather the sun back in the air under the sprinkler or spray mist can also be artificial rainbow. 　
The size of water droplets in the air, determines the color of the rainbow and width. Large droplets in the air, on the bright rainbow. Relatively narrow; the other hand, water droplets small rainbow color on the short and relatively wide. We do not see the face of the sun is the rainbow, only 100 behind the sun to see the Rainbow, so the morning rainbow appeared in the West, the evening of the total rainbow appeared in the East. Can we see, only by plane from a height and look down to see. Hong appearance and associated changes in the weather at that time, the general from the rainbow appears in the sky can be estimated at the time of the location will be sunny or rainy days. Rainbow appears when the East 　
Local is not easy to rain, and the rainbow appears when the West, the possibility of local rain is great. 　
Obviously the extent of the rainbow, depending on the size of the air small and medium-sized water droplets, the greater the size of small water droplets to form more bright rainbow, the smaller the size of small water droplets to form a rainbow is not clear. Generally lower temperatures in winter, there is not easy in the air in small droplets, the less the chance of showers, so there will be no ordinary winter rainbow appeared. 　
Caused by the optical principle of the Rainbow will see the two often appear at the same time the Rainbow, in the usual concentric rainbow appeared outside, but dark, vice Hong (also known as Ni). Vice rainbow in the sun in the water droplets formed by the two reflex. The two strongest reflection in the reflection angle of 50 ° to 53 °, so the location of the Deputy rainbow outside the primary rainbow. Because there are two reflection order of the Deputy rainbow of colors with inverted main rainbow, blue outside, the inside is red. In fact, Vice rainbow rainbow there must follow the Lord, but because of its relatively low light intensity, 　
So sometimes it is not the naked eye to detect. Double rainbow over Scotland in 1307 when the Rainbow has been raised in Europe by the water droplets on the sun caused by refraction and reflection. Descartes in 1637 found that the size of water droplets will not affect the refraction of light. The ball into his glass of water to carry out experiments, to draw water to light the refractive index, using the mathematical proof of the main rainbow is a rainbow of water caused by the reflection point, and vice rainbow is caused by the two reflex. He accurately calculate the angle of the Rainbow, but was unable to explain the colorful rainbow color. Newton was a mirror glass display Link to scatter sunlight into color after the formation of the Rainbow Optical principle of all was found. 　
Rainbow does not appear in the specific location of the air. It is an observer to see optical phenomena, the location of Rainbow looks will change as the observer. When observers see the rainbow, its location must be in the opposite direction of the sun. Rainbow arch within the central, in fact, is reflective water droplets, enlarged image of the sun. Therefore, within the rainbow over the sky brighter than the rainbow. Rainbow is the center of the arch, just the direction of observer head shadow, Hong observers of their own in the shadow of the head and eyes above the line 40 ° to 42 ° position. Because 　
This when the sun is higher than 42 degrees in the air, the rainbow will be the location can be seen on the horizon rather than the following. This is why the rainbow appears little reason at noon. 　
Rainbow from one end to the other side, across the 84 °. 35mm cameras in general, the need for a focal length of 19mm wide-angle lens of the following can be used only a single cell to take the whole rainbow. If the aircraft will see the rainbow will be the original rather than the whole of the round arch, and the center of a circular rainbow is the road the direction of the aircraft. 　
Hong night is a rare phenomenon, a strong night in the moonlight that may arise. Because human vision at night under low-light hours it is difficult to do color, it looks like late Rainbow is white

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