D．Days with the Moon should never be missed.

　　解析：选C　细节理解题。由第三段中的"A search can be done at any time providing there is no bright Moon."可知，只要没有月亮，每一天对彗星猎人来说都一样可以观测。

　　3．Which of the following is a smart idea for comet hunters?

　　A．Paying more attention in the morning than in the afternoon.

　　B．Being equally serious both in the morning and afternoon.

　　C．Being more relaxed in the morning than in the afternoon.

　　D．Forming a habit of working only in the morning.

　　解析：选B　推理判断题。由第四段中的"Thus the smart comet hunter should make sure that morning activity receives as much if not more attention than any evening effort."可知，早晚观测彗星应该投入一样的精力。

　　4．What can be inferred about the CCD technology?

　　A．It's similar to a telescope.

　　B．It'll disappoint comet hunters.

　　C．It's spreading all over the world.

　　D．It'll make comet hunters feel lucky.

　　解析：选B　推理判断题。由最后一段中的"the use of advanced CCD technology ...greatly reduce the chances of new comets being found with small telescopes"可知，这种技术降低了追星猎人发现新的彗星的概率，因此他们应该会感到有些失望。

　　B

　　Edmund Halley was an English scientist who lived over 200 years ago.He studied the observations of comets which other scientists had made.The orbit of one particular comet was a very difficult mathematical (数学上的) problem.He could not figure it out.Neither could other scientists who dealt with such problems.

　　However, Halley had a friend named Newton, who was a brilliant mathematician.Newton thought he had already worked out that problem, but he could not find the papers on which he had done it.He told Halley that the orbit of a comet had the shape of an ellipse (椭圆)．

　　Now Halley set to work.He figured out (解决；计算出) the orbits of some of the comets that had been observed by scientists.He made a surprising discovery.The comets that had appeared in the years 1531, 1607, and 1682 all had the same orbit.Yet their appearances had been 75 to 76 years apart.

This seemed very strange to Halley.The different comets followed the same orbit.The more halley thought about it, the more he thought that there had not been three different comets, as people thought.He decided that they had simply seen the same comet three times.The comet had gone away and had come back again.