Passage Three
For 150 years scientists have tried to determine the solar constant, the amount of solar energy that reaches the Earth. Yet, even in the most cloud-free regions of the planet, the solar constant cannot be measured precisely. Gas molecules and dust particles in the atmosphere absorb and scatter sunlight and prevent some wavelengths of the light from ever reaching the ground.
With the advent of satellites, however, scientists have finally been able to measure the Sun’s output without being impeded by the Earth’s atmosphere. Solar Max, a satellite from the National Aeronautics and Space Administration (NASA), has been measuring the Sun’s output since February 1980. Although a malfunction in the satellite’s control system limited its observation for a few years, the satellite was repaired in orbit by astronauts from the space shuffle in 1984. Max’s observations indicate that the solar constant is not really constant after all.
The satellite’s instruments have detected frequent, small variations in the Sun’s energy output, generally amounting to no more than 0.05 percent of the Sun’s mean energy output and lasting from a few days to a few weeks. Scientists believe these fluctuations coincide with the appearance and disappearance of large groups of sunspots on the Sun’s disk. Sunspots are relatively dark regions on the Sun’s surface that have strong magnetic fields and a temperature about 2,000 degrees Fahrenheit cooler than the rest of the Sun’s surface. Particularly large fluctuations in the solar constant have coincided with sightings of large sunspot groups. In 1980, for example, Solar Max’s instruments registered a 0.3 percent drop in the solar energy reaching the Earth. At that time a sunspot group covered about 0.6 percent of the solar disk, an area 20 times larger than the Earth’s surface.
Long-term variations in the solar constant are more difficult to determine. Although Solar Max’s data have indicated a slow and steady decline in the Sun’s output, some scientists have thought that the satellite’s aging detectors might have become less sensitive over the years, thus falsely indicating a drop in the solar constant. This possibility was dismissed, however, by comparing solar Max’s observations with data from a similar instrument operating on NASA’s Nimbus 7 weather satellite since 1978.
According to the passage, scientists believe variations in the solar constant are related to ________.
【文章大意】
150 年以来科学家们一直尝试去确定太阳常数（即到达地球的太阳能总量），然而由 于云、气体分子和尘粒对太阳光的吸收、分散和阻止，直到卫星出现，科学家们才最终 能测量太阳输出的能量。不过，美国宇航局的卫星 Solar Max 观测结果表明太阳常数事 实上根本不是不变的。
细节事实题。由第三段中“Scientists believe these fluctuations coincide with the appearance and disappearance of large groups of sunspots on the Sun’s disk.科学家们 认为这些波动（即太阳常数的波动）与太阳圆面上大批太阳黑子的出现和消失同 时发生。”的对应可知 A 项“太阳黑子的活动”正确。B 项“不寻常的天气模式”； C 项“增加的尘埃水平”；D 项“地球温度的波动”。
Why is it not possible to measure the solar constant accurately without a satellite?
细节事实题。由第一段中“Gas molecules and dust particles in the atmosphere absorb and scatter sunlight and prevent some wavelengths of the light from ever reaching the ground. 气体分子和大气中的尘粒吸收、分散太阳光，且阻止一些波的太阳光到 达地球。”与第二段中“With the advent of satellites, however, scientists have finally been able to measure the Sun’s output without being impeded by the Earth’s atmosphere.然而，随着卫星的出现，科学家们最终能测量太阳输出的能量而不受 地球大气的阻碍。”的对应可知 D 项“地球的大气干扰太阳光”正确。A 项“地 球离太阳太远”；B 项“地球上的一些地区比其它地区接收更多的太阳能”；C 项 “白天的太阳光不充足”。
Why did scientists think that Solar Max might be giving unreliable information?
细节事实题。由最后一段中“some scientists have thought that the satellite’s aging detectors might have become less sensitive over the years, thus falsely indicating a drop in the solar constant.一些科学家认为，这个卫星（即 Solar Max）不断老化的 检测器多年来可能变得不那么灵敏，从而错误地表明太阳常数下降。”的对应可 知 B 项“卫星 Solar Max 的仪器正在老化”正确。A 项“卫星 Solar Max 在最初 的几年不能工作”；C 项“航天飞机不能修理卫星 Solar Max 的仪器”；D 项“雨 云 7 号气象卫星干扰卫星 Solar Max 的检测器”。
The attempt to describe the solar constant can best be described as ________.
推理判断题。由第一段中“For 150 years scientists have tried to determine the solar constant, the amount of solar energy that reaches the Earth. 150 年以来科学家们一直 尝试去确定太阳常数（即到达地球的太阳能总量）”与最后一段中“Long-term variations in the solar constant are more difficult to determine.太阳常数的长期变化 更难以确定”的对应可推知 A 项“一项持续的研究工作”正确。B 项“一个永远 无法回答的问题”；C 项“一个已经被解决了的问题”；D 项“在历史上令人关注， 但与当代的关注却无关”。
What does this passage mainly discuss?
推理判断题。由第一段中“For 150 years scientists have tried to determine the solar constant, the amount of solar energy that reaches the Earth. 150 年以来科学家们一直 尝试去确定太阳常数（即到达地球的太阳能总量）”提出对太阳常数的测量和后 续段落围绕“对太阳常数变化的测量”进行论述知 C 项“对太阳常数变化的测量” 正确。A 项“地球大气的成分”；B 项“一颗气象卫星的发射”；D 项“太阳光和 大气污染的相互作用”。
【长难句剖析】
1. With the advent of satellites, however, scientists have finally been able to measure the Sun’s output without being impeded by the Earth’s atmosphere.
【参考译文】然而，随着卫星的出现，科学家们最终能测量太阳输出的能量而不受 地球大气的阻碍。
【结构分析】句子主干为“scientists have finally been able to measure the Sun’s output”；“without being impeded by the Earth’s atmosphere”为条件状语；“With the advent of satellites”为方式状语。
2. Sunspots are relatively dark regions on the Sun’s surface that have strong magnetic fields and a temperature about 2,000 degrees Fahrenheit cooler than the rest of the Sun’s surface.
【参考译文】太阳黑子是太阳表面比较暗的区域，这些区域有着强的磁场且温度比 地球表面的其它区域低 2000 华氏度。
【结构分析】句子主干为“Sunspots are relatively dark regions”；“on the Sun’s surface” 为地点状语；“that have strong magnetic fields and a temperature about 2,000 degrees Fahrenheit cooler than the rest of the Sun’s surface”为 that 引导的从句充当“dark regions” 的后置定语。
3. Although Solar Max’s data have indicated a slow and steady decline in the Sun’s output, some scientists have thought that the satellite’s aging detectors might have become less sensitive over the years, thus falsely indicating a drop in the solar constant.
【参考译文】尽管卫星 Solar Max 的数据表明太阳输出能量缓慢且稳定的下降，但 是一些科学家认为，该卫星不断老化的检测器多年来可能变得不那么灵敏，从而错误地 表明太阳常数下降。
【结构分析】句子主干为“some scientists have thought…”；“that the satellite’s aging detectors might have become less sensitive over the years”为 that 引导的从句充当“thought” 的宾语；“thus falsely indicating a drop in the solar constant”为分词短语充当结果状语。