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11.如果地球周围没有大气层,在地球上就不可能目视观测到:A.流星;B.行星;C.恒星;D.彗星。[答案]A [解题思路]解这道題的关键是弄清楚什么天体同大气摩擦燃烧而产生光迹,划过长空。在这四种天体中,恒星是由炽热气体组成的,能自己发光的球状天体。行星本身虽然不发射可见光,但它以表面反射太阳光而发亮。彗星接近太阳的时候,彗核中的冰物质升华而成气体,在它的周围形成云雾状的彗发,彗发中的气体和微尘,被太阳风推斥,在背向太阳的一面形成一条很长的彗尾。从以上分析得知:如果地球周围没有大气层,在地球上
11. If there is no atmosphere around the Earth, it is impossible to observe it visually on Earth: A. Meteors; B. Planets; C. Stars; D. Comets. [Answer] A [Solve ideas] The key to solving this problem is to figure out what celestial bodies are burning with the atmosphere and produce light traces that cross the sky. In these four objects, the stars are spherical bodies that consist of hot gases and can emit light by themselves. Although the planet itself does not emit visible light, it shines on the surface reflecting sunlight. As the comet approaches the sun, the ice material in the nucleus sublimates into gas, forming a cloud-like burst around it. The gas and dust in the spurt are repelled by the solar wind and form a line on the side facing away from the sun. A long tail. From the above analysis, we know that if there is no atmosphere around the earth, on the earth