Question 17 - According to the passage which of the following is a direct perceptual consequence of interstellar dust?The dark regions in the starry night sky are not pockets in the universe that are devoid of stars as had long been thought.
Rather, they are dark because of interstellar dust that hides the stars behind it.Optical astronomy is most directly affected, for although interstellar gas is perfectly transparent,
the dust is not.The passage very clearly establishes the fact that interstellar dust hides the stars. Therefore, it is the direct perceptual consequence of interstellar dust.Choice A - Some stars are rendered invisible to observers on Earth. Question 18 - It can be inferred from the passage that the density of interstellar material is The interstellar material, rather like terrestrial clouds, comes in all shapes and sizes.Choice E - not homogeneous throughout interstellar space(A) higher where distances between the stars are shorter -
no evidence in the passage for this.(B) equal to that of interstellar dust -
No, because the interstellar material is a combination of dust and gas.(C) unusually low in the vicinity of our Sun -
Tricky choice. Yes the density of interstellar material in the vicinity of the sun is 1000 to 10,000 times less than the best terrestrial laboratory vacuum. But this is only in comparison to terrestrial vacuum. We do not know if it is unusually low in comparison with other areas of interstellar space. (D) independent of the incidence of gaseous components -
Nowhere in the passage does it say that, but also incorrect from the scientific point of view.(E) not homogeneous throughout interstellar space -
YESQuestion 19 - It can be inferred from the passage that it is because space is so vast that It is only because of the enormous interstellar distances that so little material per unit of volume becomes so significant.Optical astronomy is most directly affected, for although interstellar gas is perfectly transparent, the dust is not.
The passage states that the vastness of space makes it possible for so little material per unit volume to obscure the stars.Choice C - stars can be far enough from Earth to be obscured even by very sparsely distributed matter(A) little of the interstellar material in it seems substantial -
The passage does not say the vastness of space makes little material seem substantial. It only says that little material can have significant effect.(B) normal units of volume seem futile for measurements of density -
the passage does not say this(C) stars can be far enough from Earth to be obscured even by very sparsely distributed matter -
YES(D) interstellar gases can, for all practical purposes, be regarded as transparent -
the passage does not tie the transparency of the interstellar gases to the vastness of space, and also from the scientific point of view, gases are always transparent - irrespective of the volume they occupy.(E) optical astronomy would be of little use even if no interstellar dust existed -
Wrong - Optical astronomy would benefit greatly as it is the interstellar dust hides the stars.
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