托福阅读背景材料：反射星云

 　　反射星云是靠反射附近恒星的光线而发光的，呈蓝色。反射星云的光度较暗弱，较容易观测到的例子是围绕着金牛座M45七姊妹星团的反射星云，在透明度高及无月的晚上，利用望远镜便可看到整个星团是被淡蓝色的星云包裹著的。

　　Reflection Nebula¹

　　Just weeks after NASA astronauts repaired the Hubble Space Telescope in December 1999, the Hubble Heritage Project snapped this picture of NGC 1999, a reflection nebula in the constellation² Orion.

　　1999年12月，就在NASA的宇航员修复哈勃太空望远镜后数周，哈勃遗产计划小组捕捉到这张猎户座反射星云NGC1999的照片(好记，都是1999)。

　　Like fog around a street lamp, a reflection nebula shines only because the light from an embedded³ source illuminates⁴ its dust; the nebula does not emit any visible light of its own. The nebula is famous in astronomical⁵ history because the first Herbig-Haro object was discovered immediately adjacent to it (it lies just outside the new Hubble image). Herbig-Haro objects are now known to be jets of gas ejected from very young stars.

　　反射星云就象街灯周围的雾，因为其内嵌的光 源照亮了星云中的尘埃而发亮;星云本身不发出任何可见光。这个星云在天文学史上大名鼎鼎，因为第一个被发现的HH天体(赫比格-阿罗天体)就在它附近(该 HH天体刚好不在图中)。目前所知HH天体是由非常年轻的恒星喷出的高速气流。

　　The nebula is illuminated⁶ by a bright, recently formed star, visible just to the left of center. This star is cataloged as V380 Orionis, and its white color is due to its high surface temperature of about 10,000 degrees Celsius⁷, nearly twice that of our own sun. Its mass is estimated to be 3.5 times that of the sun. The star is so young that it is still surrounded by a cloud of material left over from its formation, here seen as the NGC 1999 reflection nebula.

　　这个反射星云被一颗明亮的、新近形成的恒星 (在图像的中间偏左)照亮，该恒星编号为猎户V380，因为表面温度高达10000摄氏度(几乎是太阳的2倍)而发出白色的光芒，其质量估计是太阳的 3.5倍。这颗恒星如此年轻，以至仍被形成恒星的剩余原始材料环绕，这就是我们看到的NGC1999反射星云。

　　NGC 1999 shows a remarkable⁸ jet-black cloud near its center, located just to the right and lower right of the bright star. This dark cloud is an example of a "Bok globule," named after the late University of Arizona astronomer⁹ Bart Bok. The globule is a cold cloud of gas, molecules¹⁰ and cosmic dust, which is so dense¹¹ it blocks all of the light behind it. The globule is seen silhouetted¹² against the reflection nebula illuminated by V380 Orionis. Astronomers¹³ believe that new stars may be forming inside Bok globules, through the contraction¹⁴ of the dust and molecular¹⁵ gas under their own gravity.

　　NGC1999的中心附近有一个不寻常的黑色喷流云，在图中亮恒星的右下一点点。这个暗云是一个“博克球状体”，以亚利桑那大学天文学家Bart Bok命名。该球状体是一团非常稠密的冷气体、分子、尘埃组成的云气，挡住了它后面所有的光，在被V380照亮的反射星云衬托下显示出它的轮廓。天文学家相信博克球状体内的尘埃和分子云气会在自身引力作用下收缩，然后形成新的恒星。

1 nebula   

n.星云，喷雾剂

参考例句：

• A powerful telescope can resolve a nebula into stars.一架高性能的望远镜能从星云中分辨出星球来。
• A nebula is really a discrete mass of innumerous stars.一团星云实际上是无数星体不连续的集合体。

2 constellation   

n.星座n.灿烂的一群

参考例句：

• A constellation is a pattern of stars as seen from the earth. 一个星座只是从地球上看到的某些恒星的一种样子。
• The Big Dipper is not by itself a constellation. 北斗七星本身不是一个星座。

3 embedded   

a.扎牢的

参考例句：

• an operation to remove glass that was embedded in his leg 取出扎入他腿部玻璃的手术
• He has embedded his name in the minds of millions of people. 他的名字铭刻在数百万人民心中。

4 illuminates   

v.使明亮( illuminate的第三人称单数 )；照亮；装饰；说明

参考例句：

• The light shines on from over there and illuminates the stage. 灯光从那边照进来，照亮了舞台。 来自《简明英汉词典》
• The sun illuminates the sky. 太阳照亮了天空。 来自《简明英汉词典》

5 astronomical   

adj.天文学的，（数字）极大的

参考例句：

• He was an expert on ancient Chinese astronomical literature.他是研究中国古代天文学文献的专家。
• Houses in the village are selling for astronomical prices.乡村的房价正在飙升。

6 illuminated   

adj.被照明的；受启迪的

参考例句：

• Floodlights illuminated the stadium. 泛光灯照亮了体育场。
• the illuminated city at night 夜幕中万家灯火的城市

7 Celsius   

adj.摄氏温度计的，摄氏的

参考例句：

• The temperature tonight will fall to seven degrees Celsius.今晚气温将下降到七摄氏度。
• The maximum temperature in July may be 36 degrees Celsius.七月份最高温度可能达到36摄氏度。

8 remarkable   

adj.显著的，异常的，非凡的，值得注意的

参考例句：

• She has made remarkable headway in her writing skills.她在写作技巧方面有了长足进步。
• These cars are remarkable for the quietness of their engines.这些汽车因发动机没有噪音而不同凡响。

9 astronomer   

n.天文学家

参考例句：

• A new star attracted the notice of the astronomer.新发现的一颗星引起了那位天文学家的注意。
• He is reputed to have been a good astronomer.他以一个优秀的天文学者闻名于世。

10 molecules   

分子( molecule的名词复数 )

参考例句：

• The structure of molecules can be seen under an electron microscope. 分子的结构可在电子显微镜下观察到。
• Inside the reactor the large molecules are cracked into smaller molecules. 在反应堆里，大分子裂变为小分子。

11 dense   

a.密集的，稠密的，浓密的；密度大的

参考例句：

• The general ambushed his troops in the dense woods. 将军把部队埋伏在浓密的树林里。
• The path was completely covered by the dense foliage. 小路被树叶厚厚地盖了一层。

12 silhouetted   

显出轮廓的，显示影像的

参考例句：

• We could see a church silhouetted against the skyline. 我们可以看到一座教堂凸现在天际。
• The stark jagged rocks were silhouetted against the sky. 光秃嶙峋的岩石衬托着天空的背景矗立在那里。

13 astronomers   

n.天文学者，天文学家( astronomer的名词复数 )

参考例句：

• Astronomers can accurately foretell the date,time,and length of future eclipses. 天文学家能精确地预告未来日食月食的日期、时刻和时长。 来自《简明英汉词典》
• Astronomers used to ask why only Saturn has rings. 天文学家们过去一直感到奇怪，为什么只有土星有光环。 来自《简明英汉词典》

14 contraction   

n.缩略词，缩写式，害病

参考例句：

• The contraction of this muscle raises the lower arm.肌肉的收缩使前臂抬起。
• The forces of expansion are balanced by forces of contraction.扩张力和收缩力相互平衡。

15 molecular   

adj.分子的；克分子的

参考例句：

• The research will provide direct insight into molecular mechanisms.这项研究将使人能够直接地了解分子的机理。
• For the pressure to become zero, molecular bombardment must cease.当压强趋近于零时，分子的碰撞就停止了。