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In the 1980's,astronomer BohdanPaczynski proposed a way of determining whether the enormousdark haloconstituting the outermost part of the Milky Way galaxy is composed of MACHO's(massive compact halo objects), which are astronomical objects too dimto bevisible.Paczynski reasoned thatifMACHO's make up this halo, a MACHO would occasionally drift in front of astarin the Large Magellanic Cloud, a bright galaxy near the Milky Way.The gravity of a MACHO that had sodrifted, astronomers agree, would cause the star's light rays, which would otherwise diverge, to bend together so that, as observed from Earth, the star would temporarily appear to brighten, a process known as microlensing.Because many individual stars areofintrinsically variable brightness, some astronomers have contended that thebrighteningof intrinsically variable stars can be mistaken formicrolensing.However, whereas thedifferent colors oflight emitted by an intrinsically variable star are affecteddifferently whenthe star brightens, all of a star's colors are equally affectedbymicrolensing.Thus, if a MACHOmagnifiesa star's red light tenfold, it will do the same to the star's bluelight andyellow light.Moreover, it ishighlyunlikely that a star in the Large Magellanic Cloud will undergomicrolensingmore than once, because the chance that a second MACHO would passin front ofexactly the same star is minuscule.
Question #55.639-01 (23881-!-item-!-188;#058&000639-01)
It can be inferredfrom the passagethat which of the following would constitute the strongestevidence of themicrolensing of a star in the Large Magellanic Cloud?
(A) The brightnessof such a staris observed to vary at irregular intervals.
(B) The brighteningof such a staris observed to be of shorter duration than the brightening ofneighboringstars.
(C) The red lightof such a star isobserved to be brighter than its yellow light and its bluelight.
(D) Thered light, yellow light,and blue light of such a star are observed to bemagnified temporarily by thesame factor.
(E) The red lightof such a star isobserved to have increased tenfold.
Question #56.639-04 (23927-!-item-!-188;#058&000639-04)
According to thepassage,Paczynski's theory presumes that if MACHO's constituted the Milky Way'sdarkhalo, occasionally a MACHO would
(A) drift so as tolie in a directline between two stars in the outer Milky Way
(B)affect the light rays of a starin the Large Magellanic Cloud with the resultthat the star would seem for atime to brighten
(C) become obscuredas a result ofthe microlensing of a star in the Large Magellanic Cloud
(D) temporarilyincrease theapparent brightness of a star in the Large Magellanic Cloud byincreasing thegravity of the star
(E) magnify eachcolor in thespectrum of a star in the Large Magellanic Cloud by a differentamount
Question #57.639-06 (23973-!-item-!-188;#058&000639-06)
The passage isprimarily concernedwith
(A) outliningreasons why aparticular theory is no longer credited by some astronomers
(B) presenting datacollected by aresearcher in response to some astronomers' criticism of aparticular line ofreasoning
(C) explaining whya researcherproposed a particular theory and illustrating how influential thattheory hasbeen
(D) showing how aresearcher'stheory has been used to settle a dispute between the researcher andsomeastronomers
(E)describing a line of reasoningput forth by a researcher and addressing acontention concerning that line ofreasoning
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发表于 2011-8-5 19:31:00
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