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I agree with your explanation for selecting option E. But the only question that I cant get rid of - What if there is a 3rd type of telescope, which meets the "light-gathering capacity" feature? Logically, there cant be a 3rd category as we have covered space (i.e. outside Earth) and ground (i.e. Earth). How to avoid such questions during the exam?

ChiranjeevSingh
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Images from ground-based telescopes are invariably distorted by the Earth's atmosphere. Orbiting space telescopes, however, operating above Earth's atmosphere, should provide superbly detailed images. Therefore, ground-based telescopes will soon become obsolete for advanced astronomical research purposes.

Which of the following statements, if true, would cast the most doubt on the conclusion drawn above?


(A) An orbiting space telescope due to be launched this year is far behind schedule and over budget, whereas the largest ground-based telescope was both within budget and on schedule.

(B) Ground-based telescopes located on mountain summits are not subject to the kinds of atmospheric distortion which, at low altitudes, make stars appear to twinkle.

(C) By careful choice of observatory location, it is possible for large-aperture telescopes to avoid most of the kind of wind turbulence that can distort image quality.

(D) When large-aperture telescopes are located at high altitudes near the equator, they permit the best Earth-based observations of the center of the Milky Way Galaxy, a prime target of astronomical research.

(E) Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require telescopes with more light-gathering capacity than space telescopes can provide.



I think we still need to do justice to this well-crafted question. Here's my attempt:

I'll just focus on options B, D, and E. However, before I get to the options, let me create a parallel argument.

Students of Class 9A are invariably ill-dressed. Students of Class 9B, however, are well-dressed. Therefore, students of Class 9A will never represent the school in inter-school competitions.

While this argument is not parallel to the original argument in every nuance, I believe it captures the essence of the original argument. If you do not agree, feel free to let me know.

Now, let me create parallel options for this argument:

Option B: Students of Class 9A mentored by their class-teacher do not have the kinds of dressing problems that make students look like beggars.

Does this option weaken the above argument?

The answer is NO. The reason is that this option says that some students of Class 9A (i.e. students mentored by the class-teacher) do not have some kinds of dressing problems. Okay. So, these students are probably better than other students of Class 9A in this respect. However, vis-a-vis students of Class 9B, are these students comparable? There is no indication of this comparison. The reasoning of the argument still holds as is. Even though these students do not have certain kinds of dressing problems, they still are ill-dressed, as originally stated in the argument. Thus, it still doesn't make any sense to ask these students to represent the school. Think about it. The reasoning in the argument was that students of Class 9A are shabby and students of Class 9B are not and that thus students of Class 9A will not represent the school. Even if some students of Class 9A are less shabby than some other students of Class 9A, all the students of Class 9A are still shabby, and thus the reasoning of the argument is still intact.

Similarly, the given option B just says that certain ground-based telescopes (i.e. located on mountain summits) do not have 'certain' kinds of distortions. However, they still have distortions as should every ground-based telescope have (given the facts in the passage). Thus, the reasoning of the argument still holds as is.

Option D (The Parallel form): When students of Class 9A are mentored by their class teacher, they become the best-dressed of the students of Class 9A.

Again, in this option too, just as in option B, we are comparing shabbiness or the sense of dressing among the students of Class 9A. We still are not presenting any advantage students of Class 9A have over students of Class 9B. Of course, if we rank some students of Class 9A in terms of their dressing sense, some students are going to come at the top. However, this doesn't have any effect on the given fact that all students of Class 9A are ill-dressed. Thus, the reasoning of the argument still stands as is.

Similarly, the given option D says that the telescopes located at high altitudes near the equator provide the best 'Earth-based' observations (not the best 'overall' - in which case this option will present an advantage of ground-based telescopes over space telescopes and thus will weaken the argument). Comparing different ground-based telescopes will not help; of course, some of them will be better than the others. However, they all are invariably inferior to the orbiting space telescopes, as stated in the passage. Thus, the reasoning of the passage holds as is.

Option E: This option presents a shortcoming of the orbiting space telescopes. Let me also state that this shortcoming is with respect to ground-based telescopes, not a shortcoming in general. Why do I say that this shortcoming is w.r.t ground-based telescopes?

Because of what the non-essential modifier(within double commas) means. The modifier means that the astronomers rely upon detailed spectral analyses for determining the chemical composition and evolutionary history of stars. If they rely on this capability for determining X (chemical composition etc), they must already be having this capability because, from the context, it seems that they are already determining the chemical composition and evolutionary history of stars. Now, if they have this capability and the orbiting space telescopes cannot provide this capability, it's likely that ground-based telescopes currently provide this capability. Thus, this option presents an advantage ground-based telescopes have over orbiting space telescopes and thus gives us a reason to doubt that ground-based telescopes will become obsolete.

I hope it helps!

- CJ
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We don't have to worry about a third type of telescope, because we are not trying to prove that ground-based are necessary. We just need to show that space telescopes will not make ground telescopes obsolete. When we use E to defend the ground ones against the space ones, then the argument is effectively broken until we have some new reason to say that ground scopes will become obsolete. Sure, perhaps some other type of telescope will be better than both and will make them both obsolete. But we don't have that information. Based on what we have, the threat from space-based is eliminated, and we don't have reason to say that ground-based are out.
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(E) Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require telescopes with more light-gathering capacity than space telescopes can provide.

-- Can someone please explain how do we relate "telescopes with more light-gathering capacity" with Ground based telescopes ?

Had the option mentioned Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require Ground based telescopes with more light-gathering capacity than space telescopes can provide. --> This would have been correct.
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(E) Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require telescopes with more light-gathering capacity than space telescopes can provide.

-- Can someone please explain how do we relate "telescopes with more light-gathering capacity" with Ground based telescopes ?

Had the option mentioned Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require Ground based telescopes with more light-gathering capacity than space telescopes can provide. --> This would have been correct.
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Hi Yudhajit22,

We should look at the whole thing:

E. Detailed spectral analyses... require telescopes with more light-gathering capacity than space telescopes can provide.

If space telescopes can't provide the light-gathering capacity that DSA needs, and astronomers are already using DSA (since they rely on DSA), surely the only (reasonable) alternative is ground-based telescopes?
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Yes that makes sense , thankyou !!
AjiteshArun
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(E) Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require telescopes with more light-gathering capacity than space telescopes can provide.

-- Can someone please explain how do we relate "telescopes with more light-gathering capacity" with Ground based telescopes ?

Had the option mentioned Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require Ground based telescopes with more light-gathering capacity than space telescopes can provide. --> This would have been correct.
Hi Yudhajit22,

We should look at the whole thing:

E. Detailed spectral analyses... require telescopes with more light-gathering capacity than space telescopes can provide.

If space telescopes can't provide the light-gathering capacity that DSA needs, and astronomers are already using DSA (since they rely on DSA), surely the only (reasonable) alternative is ground-based telescopes?
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Images from ground-based telescopes are invariably distorted by the Earth's atmosphere. Orbiting space telescopes, however, operating above Earth's atmosphere, should provide superbly detailed images. Therefore, ground-based telescopes will soon become obsolete for advanced astronomical research purposes.

Which of the following statements, if true, would cast the most doubt on the conclusion drawn above?


(A) An orbiting space telescope due to be launched this year is far behind schedule and over budget, whereas the largest ground-based telescope was both within budget and on schedule.

(B) Ground-based telescopes located on mountain summits are not subject to the kinds of atmospheric distortion which, at low altitudes, make stars appear to twinkle.

(C) By careful choice of observatory location, it is possible for large-aperture telescopes to avoid most of the kind of wind turbulence that can distort image quality.

(D) When large-aperture telescopes are located at high altitudes near the equator, they permit the best Earth-based observations of the center of the Milky Way Galaxy, a prime target of astronomical research.

(E) Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require telescopes with more light-gathering capacity than space telescopes can provide.


Show Spoiler
Answer Key

Two controversial choices (for me)

(B) Ground-based telescopes on mountain summits are still subject to more atmospheric distortion than are space telescopes orbiting above the atmosphere.

(E) CORRECT. This indicates an inherent limitation of space-based telescopes: unlike Earth-based telescopes, they lack the light-gathering capacity that astronomers need to perform one of their primary tasks, i.e., detailed spectral analyses. So Earth-based telescopes are unlikely to soon become obsolete.

Show Spoiler
My Reasoning:

My initial answer was (B), and still is. As for answer choice (E), I'm unconvinced because the answer choice doesn't point out unambiguously that Earth-based telescopes have that light-gathering capacity that space-based telescopes fall short, even though the explanation just inexplicably claims that capacity for Earth-based telescopes. As a non-expert in this field, I suppose the test takers aren't supposed to infer that space-based and Earth-based telescopes are only two categories of telescopes in a dichotomy, or that Earth-based telescopes inherently have a better light-gathering capacity that the space-based ones.

As for answer (B), from the viewpoint of a domain illiterate, the reference of "make stars appear to twinkle" doesn't come over as downright inferior and worth being rendered obsolete; the answer actually came over as "The problem with atmospheric distortion becomes abated, to whatever extent, when ground-based telescopes are located on mountain summits; hence, can still be of some use". My choice of (B) over (E) bases primarily on the fact that (E) doesn't explicitly claim for ground-based telescopes the capacity that would make it more useful than space-based ones in that particular regard, while (B) explicitly points out how the weakness of ground-based telescopes can be offset.

Thank you : )

SOLUTION
Passage Analysis

Images from ground-based telescopes are invariably distorted by the Earth's atmosphere.
• Telescopes based on land provide images that are distorted by the air around the earth.
Orbiting space telescopes, however, operating above Earth's atmosphere, should provide superbly detailed images.
• Telescopes in space orbit the earth and work above the atmosphere. Therefore, they should give detailed images not distorted by the atmosphere.
Therefore, ground-based telescopes will soon become obsolete for advanced astronomical research purposes.
• Thus, ground-based telescopes will stop being used for advanced research in astronomy.

Question stem Analysis
Which of the following statements, if true, would cast the most doubt on the conclusion drawn above?
This is a weaken question stem. We should cast doubt on the conclusion that ground-based telescopes will become obsolete for advanced astronomical research.

Prethinking

Weaken framework
What new information can decrease one’s belief in the conclusion that that ground-based telescopes will become obsolete for advanced astronomical research, given that space telescope images are not distorted by the atmosphere and can give superbly detailed images?

Weakener 1- Ground-based telescopes have some advantages that space-based telescopes do not have which is relevant for advanced research.
Weakener 2- Space telescopes have some significant disadvantage that makes them not suitable for advanced research, despite the lack of atmospheric distortion

Option Analysis

(A) An orbiting space telescope due to be launched this year is far behind schedule and over budget, whereas the largest ground-based telescope was both within budget and on schedule.
This statement points out only specific incidents and does not give any indication on why ground-based telescopes will not be obsolete. If space telescopes are more affordable then they should be at an advantage according to this option. Hence this is an incorrect answer.

(B) Ground-based telescopes located on mountain summits are not subject to the kinds of atmospheric distortion which, at low altitudes, make stars appear to twinkle.
This option says ground-based telescopes can evade atmospheric distortion of the type that leads to the twinkling of stars when placed on mountain summits. But we still do not know if all the atmospheric distortions can be avoided, we still do not know if placing these on summits will provide the superbly detailed images needed. Hence this option cannot weaken the claim as well.

(C) By careful choice of observatory location, it is possible for large-aperture telescopes to avoid most of the kind of wind turbulence that can distort image quality.
Wind turbulence may not be the only factor that affects the image quality inside the atmosphere. Hence even if that is avoided, we cannot say the output will be at par with space telescopes. Hence this option is also incorrect.

(D) When large-aperture telescopes are located at high altitudes near the equator, they permit the best Earth-based observations of the center of the Milky Way Galaxy, a prime target of astronomical research.
This option specifies a particular location for a particular observation from the earth. But we need to compare ground telescope observations with space telescope observations to be relevant in this context. The absolute best earth-based observation may still be poorer than space-based observation. Hence this answer is incorrect.

(E) Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require telescopes with more light-gathering capacity than space telescopes can provide.
Option E, in line with our weakener 2, provides a situation that is a disadvantage of space telescopes for the purpose of astronomical research.

The correct answer is E.
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Hi,
eGMAT student here.

For this question, I did not choose option E because although it just says that a space-based telescope has a certain disadvantage..period..and doesn't say ground-based satellites are better in this aspect. So, isn't it a bit too far-fetched to select this option given that Option D, which says high altitude equatorial satellites (essentially ground-based satellites), offer the "BEST" of something (better than anything, including space-based) that is a "prime target" for astronomical research. Doesn't option D tie a strengthener to the entities mentioned in the passage in a much better way?

Thanks in advance,
Vishnu.
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Not sure how the correct answer can be E, since we cannot say whether ground-based telescopes have a higher light-gathering capacity?

The stimulus mentions that images for ground-based telescopes are invariably distorted by the atmosphere, but how does that lead us to the conclusion that ground based telescopes have light-gathering capacity that space telescopes do not have?
kahipz
Images from ground-based telescopes are invariably distorted by the Earth's atmosphere. Orbiting space telescopes, however, operating above Earth's atmosphere, should provide superbly detailed images. Therefore, ground-based telescopes will soon become obsolete for advanced astronomical research purposes.

Which of the following statements, if true, would cast the most doubt on the conclusion drawn above?

(A) An orbiting space telescope due to be launched this year is far behind schedule and over budget, whereas the largest ground-based telescope was both within budget and on schedule.

(B) Ground-based telescopes located on mountain summits are not subject to the kinds of atmospheric distortion which, at low altitudes, make stars appear to twinkle.

(C) By careful choice of observatory location, it is possible for large-aperture telescopes to avoid most of the kind of wind turbulence that can distort image quality.

(D) When large-aperture telescopes are located at high altitudes near the equator, they permit the best Earth-based observations of the center of the Milky Way Galaxy, a prime target of astronomical research.

(E) Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require telescopes with more light-gathering capacity than space telescopes can provide.

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This one has been discussed pretty thoroughly earlier on in the thread. Check out the 2nd page of results to see a few different takes. GMAT Ninja gets into detail on this, and here's one of my posts that covers the idea:

E tells us that there's something very important that space telescopes cannot do. We can actually infer (without assumption) that ground telescopes can fulfill this function, because if astronomers rely on this data, they must already be getting it! So unless there's some third kind of telescope (an aquatic telescope?!?), we must be getting that data from ground telescopes. But honestly, even if we didn't make that inference, we could still pick E. It's showing that space telescopes can't do everything, so that even if ground telescopes weren't currently filling this need, we might keep developing them for that purpose.
kabirgandhi
Not sure how the correct answer can be E, since we cannot say whether ground-based telescopes have a higher light-gathering capacity?

The stimulus mentions that images for ground-based telescopes are invariably distorted by the atmosphere, but how does that lead us to the conclusion that ground based telescopes have light-gathering capacity that space telescopes do not have?
kahipz
Images from ground-based telescopes are invariably distorted by the Earth's atmosphere. Orbiting space telescopes, however, operating above Earth's atmosphere, should provide superbly detailed images. Therefore, ground-based telescopes will soon become obsolete for advanced astronomical research purposes.

Which of the following statements, if true, would cast the most doubt on the conclusion drawn above?

(A) An orbiting space telescope due to be launched this year is far behind schedule and over budget, whereas the largest ground-based telescope was both within budget and on schedule.

(B) Ground-based telescopes located on mountain summits are not subject to the kinds of atmospheric distortion which, at low altitudes, make stars appear to twinkle.

(C) By careful choice of observatory location, it is possible for large-aperture telescopes to avoid most of the kind of wind turbulence that can distort image quality.

(D) When large-aperture telescopes are located at high altitudes near the equator, they permit the best Earth-based observations of the center of the Milky Way Galaxy, a prime target of astronomical research.

(E) Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require telescopes with more light-gathering capacity than space telescopes can provide.

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Hey Dimitry,

Thanks for this explanation - I think this is one of those CR questions where the GMAC doesn't necessarily do the best job, the right answer seems poorly worded to me. However, I think this explanation points to how, in some of the hardest CR questions, intuition + POE can really help narrow choices down, increasing your probability of getting an informed guess correct
DmitryFarber
This one has been discussed pretty thoroughly earlier on in the thread. Check out the 2nd page of results to see a few different takes. GMAT Ninja gets into detail on this, and here's one of my posts that covers the idea:

E tells us that there's something very important that space telescopes cannot do. We can actually infer (without assumption) that ground telescopes can fulfill this function, because if astronomers rely on this data, they must already be getting it! So unless there's some third kind of telescope (an aquatic telescope?!?), we must be getting that data from ground telescopes. But honestly, even if we didn't make that inference, we could still pick E. It's showing that space telescopes can't do everything, so that even if ground telescopes weren't currently filling this need, we might keep developing them for that purpose.
kabirgandhi
Not sure how the correct answer can be E, since we cannot say whether ground-based telescopes have a higher light-gathering capacity?

The stimulus mentions that images for ground-based telescopes are invariably distorted by the atmosphere, but how does that lead us to the conclusion that ground based telescopes have light-gathering capacity that space telescopes do not have?
kahipz
Images from ground-based telescopes are invariably distorted by the Earth's atmosphere. Orbiting space telescopes, however, operating above Earth's atmosphere, should provide superbly detailed images. Therefore, ground-based telescopes will soon become obsolete for advanced astronomical research purposes.

Which of the following statements, if true, would cast the most doubt on the conclusion drawn above?

(A) An orbiting space telescope due to be launched this year is far behind schedule and over budget, whereas the largest ground-based telescope was both within budget and on schedule.

(B) Ground-based telescopes located on mountain summits are not subject to the kinds of atmospheric distortion which, at low altitudes, make stars appear to twinkle.

(C) By careful choice of observatory location, it is possible for large-aperture telescopes to avoid most of the kind of wind turbulence that can distort image quality.

(D) When large-aperture telescopes are located at high altitudes near the equator, they permit the best Earth-based observations of the center of the Milky Way Galaxy, a prime target of astronomical research.

(E) Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require telescopes with more light-gathering capacity than space telescopes can provide.

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how is E weakening conclusion? anybody?

Images from ground-based telescopes are invariably distorted by the Earth's atmosphere. Orbiting space telescopes, however, operating above Earth's atmosphere, should provide superbly detailed images. Therefore, ground-based telescopes will soon become obsolete for advanced astronomical research purposes.

Which of the following statements, if true, would cast the most doubt on the conclusion drawn above?

(A) An orbiting space telescope due to be launched this year is far behind schedule and over budget, whereas the largest ground-based telescope was both within budget and on schedule.

(B) Ground-based telescopes located on mountain summits are not subject to the kinds of atmospheric distortion which, at low altitudes, make stars appear to twinkle.

(C) By careful choice of observatory location, it is possible for large-aperture telescopes to avoid most of the kind of wind turbulence that can distort image quality.

(D) When large-aperture telescopes are located at high altitudes near the equator, they permit the best Earth-based observations of the center of the Milky Way Galaxy, a prime target of astronomical research.

(E) Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require telescopes with more light-gathering capacity than space telescopes can provide.

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I think GMAC did okay here. I'd encourage you to use occasions when the answers don't seem to fit as an opportunity to fine-tune your understanding of what the questions are looking for. Since the argument predicted that space-based telescopes would make ground-based telescopes obsolete, it would be reasonable for us to expect a weaken that showed that space-based could not fully replace ground-based. Any new information that shows a liability or gap in what space-based telescopes can do would be a good weaken. From that perspective, E fits the bill very well.

adithya000, take a look at the discussion we've been having about E and let us know if you have questions. There are also quite a few posts about E in the second page of results.
kabirgandhi
Hey Dimitry,

Thanks for this explanation - I think this is one of those CR questions where the GMAC doesn't necessarily do the best job, the right answer seems poorly worded to me. However, I think this explanation points to how, in some of the hardest CR questions, intuition + POE can really help narrow choices down, increasing your probability of getting an informed guess correct
DmitryFarber
This one has been discussed pretty thoroughly earlier on in the thread. Check out the 2nd page of results to see a few different takes. GMAT Ninja gets into detail on this, and here's one of my posts that covers the idea:

E tells us that there's something very important that space telescopes cannot do. We can actually infer (without assumption) that ground telescopes can fulfill this function, because if astronomers rely on this data, they must already be getting it! So unless there's some third kind of telescope (an aquatic telescope?!?), we must be getting that data from ground telescopes. But honestly, even if we didn't make that inference, we could still pick E. It's showing that space telescopes can't do everything, so that even if ground telescopes weren't currently filling this need, we might keep developing them for that purpose.
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In this question, the conclusion is that: since space orbiting telesscopes provide more detailed images than ground based telescopes, ground based telescopes will be obsolete for astronomical research.

As we can see, the author makes a jump, and we can quickly pre-think the assumption that the author makes: There is no use ground based telescopes, that space orbiting telescopes do not have.

Hence a weakener would have to tell us something that ground based telescopes do exclusively, or better than space orbiting telescopes.

Choice D: When large-aperture telescopes are located at high altitudes near the equator, they permit the best Earth-based observations of the center of the Milky Way Galaxy, a prime target of astronomical research.

This choice mentions that there is something that large aperture/ground based telescopes permit the best observations of something that is a prime target or astronomical research.

I believe that since they are the "best" at something, that should be reason enough to call this a weakener, that is to say that ground based telescopes are not going to become obsolete for astronomical research.

Choice E: Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require telescopes with more light-gathering capacity than space telescopes can provide.

This tells us that there is some functionality that space telescopes lack, but we do not know whether ground based telescopes have this functinality to begin with. Hence, in my opinion, this does not weaken the conclusion that ground based telescopes will soon be obsolete.

Good analogy for what this choice says:

Conclusion: Bikes are going to be obsolete because cars are better.

Incorrect Weakener: But cars can't fly

We cannot choose this because we do not know whether bikes can fly either.

Correct Weakener: Bikes are the best mode of transport for navigating through heavy traffic.

Can anyone help me understand whether my reasoning is flawed?

[b]KarishmaB Bunuel @WhitEngagePrep[/b]
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Images from ground-based telescopes are invariably distorted by the 09 Oct 2025, 07:57
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kabirgandhi
In this question, the conclusion is that: since space orbiting telesscopes provide more detailed images than ground based telescopes, ground based telescopes will be obsolete for astronomical research.

As we can see, the author makes a jump, and we can quickly pre-think the assumption that the author makes: There is no use ground based telescopes, that space orbiting telescopes do not have.

Hence a weakener would have to tell us something that ground based telescopes do exclusively, or better than space orbiting telescopes.

Choice D: When large-aperture telescopes are located at high altitudes near the equator, they permit the best Earth-based observations of the center of the Milky Way Galaxy, a prime target of astronomical research.

This choice mentions that there is something that large aperture/ground based telescopes permit the best observations of something that is a prime target or astronomical research.

I believe that since they are the "best" at something, that should be reason enough to call this a weakener, that is to say that ground based telescopes are not going to become obsolete for astronomical research.

Choice E: Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require telescopes with more light-gathering capacity than space telescopes can provide.

This tells us that there is some functionality that space telescopes lack, but we do not know whether ground based telescopes have this functinality to begin with. Hence, in my opinion, this does not weaken the conclusion that ground based telescopes will soon be obsolete.

Good analogy for what this choice says:

Conclusion: Bikes are going to be obsolete because cars are better.

Incorrect Weakener: But cars can't fly

We cannot choose this because we do not know whether bikes can fly either.

Correct Weakener: Bikes are the best mode of transport for navigating through heavy traffic.

Can anyone help me understand whether my reasoning is flawed?
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Let's consider choice (D):

(D) When large-aperture telescopes are located at high altitudes near the equator, they permit the best Earth-based observations of the center of the Milky Way Galaxy, a prime target of astronomical research.

Notice that (D) does not say that large-aperture telescopes located at high altitudes permit the "best" observations of the center of the Milky Way Galaxy. Rather, it says that they permit the "best Earth-based" observations.

The passage has told us that "Earth-based" observations are "invariably distorted."

So, what (D) says doesn't change what we know. After all, even if they are the best "Earth-based" observations of the center of the Milky Way, given what the passage says, they are not the best observations overall since are distorted.

Now, let's consider (E):

(E) Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require telescopes with more light-gathering capacity than space telescopes can provide.

This choice indicates that there is something space telescopes cannot be used for, "detailed spectral analysis." It doesn't say that Earth-based telescopes can be used for this purpose, but they probably can be, since common knowledge indicates that there is not a third type of telescope that could be used. In any case, since space telescopes don't serve this purpose and Earth-based ones may, this information weakens the argument by indicating that there may be something that Earth-based telescopes will continue to be used for in advanced astronomical research.

Correct answer: E
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Thanks, this is probably the most helpful explanation I have seen yet.
MartyMurray

Let's consider choice (D):

(D) When large-aperture telescopes are located at high altitudes near the equator, they permit the best Earth-based observations of the center of the Milky Way Galaxy, a prime target of astronomical research.

Notice that (D) does not say that large-aperture telescopes located at high altitudes permit the "best" observations of the center of the Milky Way Galaxy. Rather, it says that they permit the "best Earth-based" observations.

The passage has told us that "Earth-based" observations are "invariably distorted."

So, what (D) says doesn't change what we know. After all, even if they are the best "Earth-based" observations of the center of the Milky Way, given what the passage says, they are not the best observations overall since are distorted.

Now, let's consider (E):

(E) Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require telescopes with more light-gathering capacity than space telescopes can provide.

This choice indicates that there is something space telescopes cannot be used for, "detailed spectral analysis." It doesn't say that Earth-based telescopes can be used for this purpose, but they probably can be, since common knowledge indicates that there is not a third type of telescope that could be used. In any case, since space telescopes don't serve this purpose and Earth-based ones may, this information weakens the argument by indicating that there may be something that Earth-based telescopes will continue to be used for in advanced astronomical research.

Correct answer: E
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Okay i agree with you that E says that there are few limitations of Space Telescope. But how does it signal whether Ground Based Telescope will become extinct or not? May be There are some other kind of telescopes which will counter this limitation of Space Telescope so even if the Space Telescope is not 100% success it can still be the case that Ground Based Telescope may disappear in future? How does it weaken or cast doubt on the info about 'Ground Based Telescope'?

Please clarify how you jumped from 'LIMITATIONS' of Space Telescope to 'NOT DISAPPEARING' of Ground Based Telescope?
sauravleo123

Choice B is talking about a particular kind of ground based telescope.(Ground based telescope located on mountains) You dont know how much percentage of Ground based telescope constitute those that are located on the mountains.

I think you are assuming that in near future, all the Ground based telescopes can be migrated to the mountains and hence can be useful. The option does not tell you this.

Also note that, if Space based telescope are already there which can carry out this functionality without any problems that ground based telescope may face, then why will the Ground based telescope be used if same functionality can be achieved by the space based ones .


See to weaken the conclusion, we need to show something that Ground based telescope can do but space based ones cannot, so there will be a reason to use ground based telescope as you cannot achieve that functionality using the space based.


Choice E precisely does that.


It states that Space based telescope may not be useful for analyzing chemical composition of stars .So it presents one drawback for space based telescope.

This functionality can be provided (we are not sure whether ground based can provide this functionality, but still there is a chance) by ground based telescope. So it weakens the conclusion.


We do not need to falsify a conclusion. Any choice that casts some doubt on the conclusion can be a valid Weakener
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Hi mkeshri185,

Let me try to explain:


Conclusion- Ground based telescopes will soon become obsolete for advanced astronomical research purposes.

One of the ways to weaken this conclusion is saying that ground based telescopes will be essential for atleast some astronomical research activity. Despite their known limitation, they will have advantage over Space telescopes in some aspect.

That is exactly what Choice E does.

It tells us that even if ground based telescopes provide distorted images, they may still be required for detailed spectral analyses and thus they may not become obsolete.


Hope that helps!



mkeshri185
Okay i agree with you that E says that there are few limitations of Space Telescope. But how does it signal whether Ground Based Telescope will become extinct or not? May be There are some other kind of telescopes which will counter this limitation of Space Telescope so even if the Space Telescope is not 100% success it can still be the case that Ground Based Telescope may disappear in future? How does it weaken or cast doubt on the info about 'Ground Based Telescope'?

Please clarify how you jumped from 'LIMITATIONS' of Space Telescope to 'NOT DISAPPEARING' of Ground Based Telescope?

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Images from ground-based telescopes are invariably distorted by the 17 Oct 2025, 09:23
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mkeshri185
Okay i agree with you that E says that there are few limitations of Space Telescope. But how does it signal whether Ground Based Telescope will become extinct or not? May be There are some other kind of telescopes which will counter this limitation of Space Telescope so even if the Space Telescope is not 100% success it can still be the case that Ground Based Telescope may disappear in future? How does it weaken or cast doubt on the info about 'Ground Based Telescope'?

Please clarify how you jumped from 'LIMITATIONS' of Space Telescope to 'NOT DISAPPEARING' of Ground Based Telescope?
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These posts from earlier in the thread might help a bit:

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E is the only option that undermined the usage / importance of space telescopes making it the right answer
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Conclusion: Therefore, ground-based telescopes will soon become obsolete for advanced astronomical research purposes.


(E) Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require telescopes with more light-gathering capacity than space telescopes can provide.

How do I know that detailed spectral analyses mentioned in answer choice E are for advanced astronomical research purposes unless I apply outside knowledge?

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Conclusion: Therefore, ground-based telescopes will soon become obsolete for advanced astronomical research purposes.


(E) Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require telescopes with more light-gathering capacity than space telescopes can provide.

How do I know that detailed spectral analyses mentioned in answer choice E are for advanced astronomical research purposes unless I apply outside knowledge?
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You don't know for sure, but you don't need to.

The correct answer to a Weaken question does not have to indicate that the conclusion is incorrect with a high level of certainty. Rather, it has only to cast some doubt on the conclusion.

Since it seems quite possible, even likely, that "detailed spectral analyses upon which astronomers rely for determining the chemical composition and evolutionary history of stars," would be an aspect of advanced astronomical research, the fact that space telescopes do not have sufficient light-gathering capacity for such analyses casts doubt on the conclusion.

Thus, (E) Weakens the argument even if we don't know for sure that "detailed spectral analyses" are an aspect of "advanced astronomical research."
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