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  3. Because of its precision, the Cepheid-variable method of correlating

Because of its precision, the Cepheid-variable method of correlating

游客2024-01-11  39
问题            Because of its precision, the Cepheid-variable method of correlating the
       luminosity of Cepheid stars with those of known types of ordinary stars is one of
       the most important tools that astronomers have for ascertaining distances to
Line     proximate galaxies. Fortunately, Cepheids are luminous enough to be observed
(5)      in other galaxies, not just in our own, such that scientists have established a
       benchmark for their true brightness. One first observes a Cepheid, notes the
       time span for its luminance to vary, and plots that information on an already
       established graph to derive its intrinsic luminosity.  Comparing intrinsic
       luminosity with apparent brightness allows one to calculate the star’s distance
(10)     as long as the period-luminosity relation for the star in question is first corrected
       for gravitational interference, parallax, and experimental error. Data gathered
       by this process would suggest that the universe is expanding, but the method is
       less reliable in the nether reaches of the universe, where the crucial evidence
       for cosmic expansion would likely be spotted. [br] The passage is primarily concerned with
选项 A、describing an important technique
B、discussing a new method
C、investigating a controversial procedure
D、announcing a significant discovery
E、promoting a novel application
答案 A
解析
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