天象描写:天空-Sky天象描写:天空-Sky天空【内容提示】以“Sky”为题写一篇描写文。内容要点如下：①天气晴朗时仰望天空，地球好像被一个蓝色的大圆顶所覆盖。②天空之所以呈蓝色，是因为阳光射入地球大气层时起了变化。③阳光与微小的空气分子碰撞，便散射开来。散射开的光有多种颜色，这些颜色的组合便是蔚蓝色。④有时日落时天空呈红色。这时的阳光在天空中以较低的角度射来。⑤太阳在天空下落时，其光线穿过更多的空气，于是波长较长的橙色和红色也散射开来。日落时，波长较短的蓝色光不能穿透大气层，所以蓝光就看不见了。⑥站在一块地势平展的地方极目四望，天空好像处处都与地球交接。交接处叫地平线。⑦无论你往哪个方向看，地平线与你的距离总是等长。⑧无论你在何地，地球表面总是向下弯的，弯向远方；那是人们目力不及之处，这便是地平线。【作文示范】SkyWhenyoulookattheskyonaclearday,itseemsasiftheearthiscoveredbyabluedome①.Theskyisbluebecauseofwhathappenstosunlightasitenterstheearth＇satmosphere.Sunlightismadeupoflightraysofalllengths.Thelongerraysmakeupredlightandtheshorterraysmakeupbluelight.Assunlightenterstheearth＇satmosphere,itstrikesthetinymolecules②ofairandisscattered③.Thescatteredlightismadeupmostlyofviolet④,blue,alittlegreen,andalittleyellowandred.Thecombinationofthesecolorsisskyblue.Sometimesatsunsettheskylooksred.Thesunlightiscomingtowardyoufromalowerangleinthesky.Thelowerthesun,thelongeristhepaththatthelightraysmusttravelthroughtheair.Theshorterblueraysarescatteredimmediatelywhenstrikingthemoleculesofair.Thesunlightthatyouseelackstheblueandvioletraysthattheairhasscattered.Asthesungetslowerinthesky,thelightraysmustpassthroughmoreair,andsothelongerorangeandredraysalsobecomescattered.Atsunset,theshorterblueraysnevergetthroughtheatmosphere,soyoudonotseethem.Ifyoustandataplacewherethesurfaceoftheearthisflat,theskyseemstomeettheearthinanydirectionyoulook.Thepointatwhichtheskyandtheearthseemto“meet”iscalledthehorizon.Thehorizonisatthesamedistancefromyou,nomatterinwhatdirectionyoulook.Ifyouwalktowardthehorizon,youdonotgetclosertoit.Nomatterwhereyouare,thesurfaceoftheearthcurves⑤downwardandawayfromyou.Thedistanceatwhichyoucannolongerseetheearth＇ssurface----becauseithascurveddowntoofar----isthehorizon.【词语解释】①dome[d+um]n.圆盖；穹窿②molecule[＇m&likju:l]n.分子③scatter[＇sk$t+]v.使消散；使分散④violet[＇vai+lit]n.紫色；紫罗蓝色⑤curve[k+:v]v.成曲形；弯曲【写法指要】这是一篇科技知识小品式的天象描写文。作者以从上到下的空间顺序安排结构，先写苍穹的蔚蓝，用一个带有明喻“asif”的句型开头，写出天空像一个蓝色的大圆盖，然后以光波长短来分析天空呈蓝色的道理。接着作者写日落时天空呈红色的情景：这时的阳光在天空中以较低的角度射来，太