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  3. Scientists have taken a giant leap toward making possible the dream of building a powerful telescope on the moon that could with

Scientists have taken a giant leap toward making possible the dream of building a powerful telescope on the moon that could with

admin2018-06-06  61
问题    Scientists have taken a giant leap toward making possible the dream of building a powerful telescope on the moon that could withstand even the harshest of lunar conditions.
   Writing in Thursday’s edition of the journal Nature, they said they coated a special type of liquid surface with a layer of silver to make a highly reflective mirror like one that could be used in any future, moon-based telescope.
   "It’s the breakthrough that we need," lead researcher Ermanno Borra of Universite Laval in Quebec, Canada, said in a telephone interview. "If you want to have a liquid mirror telescope on the moon, you need the right liquid. If you don’t have the right liquid, forget it. It’s as simple as that." Borra envisions a telescope with a liquid mirror measuring 66 feet to 328 feet wide.
   Such a telescope, which has drawn NASA’s interest, could provide astronomers on Earth unprecedented views into distant reaches of the universe, studying objects far more faint even than NASA’s planned James Webb Space Telescope, due for a 2013 launch. Astronomers hope such an instrument could allow them to study the early phases of the universe after the Big Bang.
   Advocates say a large telescope on the moon would be more cheaply and easily built using a liquid mirror rather than a conventional glass one. The researchers think any liquid-mirror telescope on the moon would not come before 2020 at the earliest.
   The scientists made use of a liquid made of "ionic salts" that remains fluid at super-low temperatures. They deposited a thin layer of chromium particles on the liquid, then added a layer of silver particles to complete the mirror.
   Liquid mirror telescopes differ from conventional ones in that their primary mirrors, which gather and focus light, are made of reflective liquid instead of polished glass. The liquid can be poured into a spinning container, spreading out to make a thin, smooth, parabolic shape that can be used as a telescope mirror, the researchers said.
   The silver layer that is created is completely smooth, highly reflective, can stay stable for months, and the ionic liquid that it covers does not evaporate, the researchers said.
According to the scientists, the telescope has all of the following characteristics EXCEPT______.
选项 A、withstanding even the harshest of lunar conditions
B、studying objects for more faint than NASA’s planned James Webb Space Telescope
C、having a liquid mirror measuring 66 feet to 328 feet wide
D、being coated with a special type of liquid surface
答案B
解析
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