天象描寫(xiě):天空-Sky
天空
【內(nèi)容提示】
以“Sky”為題寫(xiě)一篇描寫(xiě)文。內(nèi)容要點(diǎn)如下：
�、偬鞖馇缋蕰r(shí)仰望天空，地球好像被一個(gè)藍(lán)色的大圓頂所覆蓋。
�、谔炜罩猿仕{(lán)色，是因?yàn)殛?yáng)光射入地球大氣層時(shí)起了變化。
�、坳�(yáng)光與微小的空氣分子碰撞，便散射開(kāi)來(lái)。散射開(kāi)的光有多種顏色，這些顏色的組合便是蔚藍(lán)色。
④有時(shí)日落時(shí)天空呈紅色。這時(shí)的陽(yáng)光在天空中以較低的角度射來(lái)。
�、萏�(yáng)在天空下落時(shí)，其光線(xiàn)穿過(guò)更多的空氣，于是波長(zhǎng)較長(zhǎng)的橙色和紅色也散射開(kāi)來(lái)。日落時(shí)，波長(zhǎng)較短的藍(lán)色光不能穿透大氣層，所以藍(lán)光就看不見(jiàn)了。
�、拚驹谝粔K地勢(shì)平展的地方極目四望，天空好像處處都與地球交接。交接處叫地平線(xiàn)。
⑦無(wú)論你往哪個(gè)方向看，地平線(xiàn)與你的距離總是等長(zhǎng)。
�、酂o(wú)論你在何地，地球表面總是向下彎的，彎向遠(yuǎn)方；那是人們目力不及之處，這便是地平線(xiàn)。
【作文示范】
Sky
When you look at the sky on a clear day, it seems as if the earth is covered by a blue dome①. The sky is blue because of what happens to sunlight as it enters the earth＇s atmosphere. Sunlight is made up of light rays of all lengths. The longer rays make up red light and the shorter rays make up blue light. As sunlight enters the earth＇s atmosphere, it strikes the tiny molecules ② of air and is scattered③. The scattered light is made up mostly of violet④, blue, a little green, and a little yellow and red. The combination of these colors is sky blue.
Sometimes at sunset the sky looks red. The sunlight is coming toward you from a lower angle in the sky. The lower the sun, the longer is the path that the light rays must travel through the air. The shorter blue rays are scattered immediately when striking the molecules of air. The sunlight that you see lacks the blue and violet rays that the air has scattered. As the sun gets lower in the sky, the light rays must pass through more air,and so the longer orange and red rays also become scattered. At sunset, the shorter blue rays never get through the atmosphere, so you do not see them.
If you stand at a place where the surface of the earth is flat, the sky seems to meet the earth in any direction you look. The point at which the sky and the earth seem to“meet”is called the horizon. The horizon is at the same distance from you, no matter in what direction you look. If you walk toward the horizon, you do not get closer to it. No matter where you are, the surface of the earth curves ⑤ downward and away from you. The distance at which you can no longer see the earth＇s surface----because it has curved down too far----is the horizon.
【詞語(yǔ)解釋】
�、賒ome [d+um] n. 圓蓋；穹窿
②molecule [＇m&likju:l] n. 分子
�、踫catter [＇sk$t+] v. 使消散；使分散
�、躹iolet [＇vai+lit] n. 紫色；紫羅藍(lán)色
�、輈urve [k+:v] v. 成曲形；彎曲
【寫(xiě)法指要】
這是一篇科技知識(shí)小品式的天象描寫(xiě)文。作者以從上到下的空間順序安排結(jié)構(gòu)，先寫(xiě)蒼穹的蔚藍(lán)，用一個(gè)帶有明喻“as if”的句型開(kāi)頭，寫(xiě)出天空像一個(gè)藍(lán)色的大圓蓋，然后以光波長(zhǎng)短來(lái)分析天空呈藍(lán)色的道理。接著作者寫(xiě)日落時(shí)天空呈紅色的情景：這時(shí)的陽(yáng)光在天空中以較低的角度射來(lái)，太陽(yáng)越低，光線(xiàn)穿過(guò)空氣的路程就越長(zhǎng)；波長(zhǎng)短的藍(lán)色碰撞空氣分子后立即散射，因此人們看不見(jiàn)，人們看到的是波長(zhǎng)較長(zhǎng)的橙色和紅色。最后，作者寫(xiě)人們站在平地上極目四望的情景：人們看到的是天地相接處的地平線(xiàn)。這樣，作者通過(guò)上、中、下三個(gè)層面的描寫(xiě)，給人們描繪出了天空呈藍(lán)色、紅色以及地平線(xiàn)形成的科學(xué)道理。