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  3. Because of its precision, the Cepheid-variable method of correlating the luminosity of Cepheid stars with those of known

Because of its precision, the Cepheid-variable method of correlating the luminosity of Cepheid stars with those of known

admin2011-01-17  74
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.
According to the passage, in the Cepheid variable method all of the following have a significant role in the calculation of the distance of a galaxy EXCEPT
选项 A、The intrinsic luminosity of a Cepheid
B、The comparative luminosity of ordinary stars
C、The observed brightness of the Cepheid
D、The data suggesting the expansion of the universe
E、The correction of the period-luminosity relation for the star being observed
答案D
解析
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