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# Images from ground-based telescopes are invariably distorted by the

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Re: Images from ground-based telescopes are invariably distorted by the  [#permalink]

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24 Aug 2017, 15:21
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shrewd1 wrote:
GMATNinja my issue with OA is that even though option E suggests that space telescopes have a drawback and cannot do a certain thing, it does not cast doubt on the argument that ground telescopes might become obsolete. maybe there would be a new kind of telescope/maybe even ground telescopes suck at that thing. We dont know!
is this not a very good quality QG question?

You are right that ground telescopes might still become obsolete, even if (E) is true. However, we do not need an answer that PROVES that ground telescopes will not become obsolete. Rather, we need an answer choice that casts the most doubt on the author's conclusion. Choice (E) directly weakens the author's argument and conclusion, so it is the best answer.
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Re: Images from ground-based telescopes are invariably distorted by the  [#permalink]

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10 Sep 2017, 01:52
sayantanc2k wrote:
smartguy595 wrote:
Really not able to convince how option E is the correct answer.

we need to assume more to chose this.

The conclusion is about a causal relation:

Space telescopes are better in one feature, and HENCE they will make earth telescopes obsolete.

Stating a negative feature of the space telescopes attacks this causal relation (though it may not directly attack the possibility that earth telescope will be obsoleted). Because space telescopes has a negative feature they will NOT be able to make the earth satellites obsolete.

If one considers "ground-based telescopes will soon become obsolete" the conclusion then your point is definitely valid. But if one considers "Superior feature of space telescope will cause ground-based telescopes to be obsolete", then option E is correct. In GMAT this causal relation as a conclusion is often tested.

For the same reason stated above option B is wrong. It does not attack the causal relation, but only supports why earth based telescopes may not be obsoleted. (Moreover, the condition that was used to prove that Space telescopes will replace earth telescopes, still holds good - even after mounting the telescopes on higher grounds, the distortion will not be eliminated, and hence the space telescopes still remain better of the two - nonetheless, this does not play any role in attacking the causal relation.)

Hi,
Plz explain how can we assume that light gathering capacity is better on ground based telescopes. The passage mentions 2 telescopes but we cant rule out that another kind of telescope may exist which contains better light gathering capacity and so, ground based telescope does not have such a feature. Also, why is option D wrong?
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10 Sep 2017, 01:55
GMATNinja wrote:
shrewd1 wrote:
GMATNinja my issue with OA is that even though option E suggests that space telescopes have a drawback and cannot do a certain thing, it does not cast doubt on the argument that ground telescopes might become obsolete. maybe there would be a new kind of telescope/maybe even ground telescopes suck at that thing. We dont know!
is this not a very good quality QG question?

You are right that ground telescopes might still become obsolete, even if (E) is true. However, we do not need an answer that PROVES that ground telescopes will not become obsolete. Rather, we need an answer choice that casts the most doubt on the author's conclusion. Choice (E) directly weakens the author's argument and conclusion, so it is the best answer.

I had the same doubt and so I eliminated option E, but I fail to understand why i8s option D incorrect? In d, we are providing an advantage feature of ground based telescope.
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30 Oct 2017, 18:17
could anyone please explain to me why option D is incorrect?
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01 Nov 2017, 10:32
Can anyone please explain for me why A is not correct? Since it seems like ground-based is much more practical than space telescope.
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01 Nov 2017, 21:46
csaluja wrote:
could anyone please explain to me why option D is incorrect?
Option D says that certain LATs provide the best Earth-based observations of the center of the Milky Way. But the fact remains that these are still "ground-based telescopes", and according to the stimulus, images from such telescopes are invariably distorted by the Earth's atmosphere. Space telescopes, on the other hand, operate outside the atmosphere. So these LATs are better at a particular task than other ground-based telescopes, but all space telescopes are better than all ground telescopes (including these LATs).
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01 Nov 2017, 21:52
oanhsokie wrote:
Can anyone please explain for me why A is not correct? Since it seems like ground-based is much more practical than space telescope.
It's a very small sample: 1 space telescope, and 1 ground-based telescope. If a lot of space telescopes were far behind schedule, then we'd doubt whether ground-based telescopes would "soon" become obsolete, but with just 1 example of each type of telescope, option A is just not strong enough. Option E attacks space telescopes as a category.
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02 Nov 2017, 23:35
Still confused why E is correct. Nowhere in the argument as well as the option E it is mentioned that ground based telescope has more light gathering capacity.
So its fine that space telescope has less light gathering capacity but how does it prevent ground based telescope to become obsolete, as they also dont solve this problem.
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05 Nov 2017, 23:22
Quote:
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.

oanhsokie wrote:
Can anyone please explain for me why A is not correct? Since it seems like ground-based is much more practical than space telescope.

Choice (A) only talks about two specific telescopes, and that is not enough data to make general statements about the practicality of each technology. Also, just because a space telescope is behind schedule and over budget does not necessarily mean that the technology is impractical or unaffordable. The planners may have underestimated the costs, but that doesn't tell us how the actual costs compare to the actual costs of ground-telescopes. Finally, space telescopes might become more cost-efficient and practical as the technology is developed. Thus, even if space telescopes are less practical now, that does not imply that they won't eventually replace ground-telescopes as costs go down.

csaluja wrote:
could anyone please explain to me why option D is incorrect?

Choice (D) just tells us the best way to use ground-based telescopes. The arrangement described might be better than any other EARTH-BASED arrangement, but if a space telescope is even better than the BEST ground-based setup, then the ground-based telescopes will likely become obsolete.
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28 Nov 2017, 19:32
kahipz wrote:
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.

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.

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 : )

conclusion: ground-based telescopes will soon become obsolete for advanced astronomical research purposes.

We will have to go with option that states or gives hope that GB telescopes will not go obsolete and will have some use. "E" captures that perfectly.

The problem with "B" is it says that the "kinds" of atmospheric distortion which makes stars twinkle and not all type of distortion, neither it gets the essence perfectly as "E" does.

Hope it helps. Thinking about the logical structures helps in this question,
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22 Dec 2017, 14:06
I agree with gmatninja,
choice B only eliminates one case in which the image distortion can occur. On the other hand, choice E tells that the space telescope has a major limit.
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24 Dec 2017, 00:16
IMO OA is E
I was confused between B and E..
But this is the reason why I chose E

(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.
-> budget is out of scope.

(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.
-> keep it

(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.
-> large aperture is out of scope. We just want to know about
ground located telescope. We do not need to know about
aperture. This just expand the argument and makes us confusing.

(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.
-> Same as C. Large aperture is out of scope.

(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.
-> keep it

B just said that distortion can be reduced. E, however, said more about research. That is the reason why I chose E.
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03 Apr 2018, 10:38
Sorry experts I just don't understand how E is the correct answer:

It just says that for more detailed studies astronomers should use telescopes with more light-gathering capacity than space telescopes can provide......... NO ONE SAYS THAT GROUND-BASED TELESCOPES CAN PROVIDE THAT CAPACITY, CHOOSING ANSWER E I HAVE TO MAKE AN IMPORTANT ASSUMPTION THAT IS NOT SPECIFIED ANYWHERE IN THE TEXT....
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03 Apr 2018, 18:56
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Fedemaravilla wrote:
Sorry experts I just don't understand how E is the correct answer:

It just says that for more detailed studies astronomers should use telescopes with more light-gathering capacity than space telescopes can provide......... NO ONE SAYS THAT GROUND-BASED TELESCOPES CAN PROVIDE THAT CAPACITY, CHOOSING ANSWER E I HAVE TO MAKE AN IMPORTANT ASSUMPTION THAT IS NOT SPECIFIED ANYWHERE IN THE TEXT....
Let's put some of the information given in the stimulus and in option E down:

1. Astronomers rely on DSA. This means that astronomers are already using DSA to determine the chemical composition and evolutionary history of stars.
2. Space telescopes cannot provide DSA; DSA can be provided only by telescopes with more light-gathering capacity than space telescopes can provide. So DSA needs non-space telescopes.

Because astronomers are already using DSA, and space telescopes can't do DSA, astronomers must be using telescopes that are not space telescopes. Such telescopes must be terrestrial (the opposite of space). Hence E is quite solid as an answer choice.

More generally, you'll find that the correct option does very often involve a "stretch". The GMAT doesn't say how much of a stretch is too much, but a little bit is okay. It'd be very hard to make a compact CR question if the question makers could not take certain things for granted. In this case, as soon as we see that E gives us a weakness (of space telescopes), we should be seriously considering it as a "candidate" option.
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08 Apr 2018, 18:29
AjiteshArun wrote:
Fedemaravilla wrote:
Sorry experts I just don't understand how E is the correct answer:

It just says that for more detailed studies astronomers should use telescopes with more light-gathering capacity than space telescopes can provide......... NO ONE SAYS THAT GROUND-BASED TELESCOPES CAN PROVIDE THAT CAPACITY, CHOOSING ANSWER E I HAVE TO MAKE AN IMPORTANT ASSUMPTION THAT IS NOT SPECIFIED ANYWHERE IN THE TEXT....
Let's put some of the information given in the stimulus and in option E down:

1. Astronomers rely on DSA. This means that astronomers are already using DSA to determine the chemical composition and evolutionary history of stars.
2. Space telescopes cannot provide DSA; DSA can be provided only by telescopes with more light-gathering capacity than space telescopes can provide. So DSA needs non-space telescopes.

Because astronomers are already using DSA, and space telescopes can't do DSA, astronomers must be using telescopes that are not space telescopes. Such telescopes must be terrestrial (the opposite of space). Hence E is quite solid as an answer choice.

More generally, you'll find that the correct option does very often involve a "stretch". The GMAT doesn't say how much of a stretch is too much, but a little bit is okay. It'd be very hard to make a compact CR question if the question makers could not take certain things for granted. In this case, as soon as we see that E gives us a weakness (of space telescopes), we should be seriously considering it as a "candidate" option.

AjiteshArun, thanks for the great response!

The other key to this question is that we are looking for something that "would cast the most doubt on the conclusion drawn above."

So we just need something that would make us question the author's logic/conclusion. The author says that space telescopes should provide superbly detailed images. Therefore, ground telescopes will soon become obsolete. In reaching the conclusion, the author is only considering image quality.

Choice (E) says, "You (author) might be right about image quality, but you haven't considered DSA." So even if we don't know that ground telescopes have the capacity needed for DSA, we already have a reason to doubt the author's logic. The author was ONLY considering image quality and failed to consider DSA.

As explained perfectly by AjiteshArun, it is very reasonable to suspect that ground telescopes have such capacity. However, even without knowing that for sure, we've already poked a hole in the author's argument. That doesn't necessarily PROVE that the author is wrong, but it certainly casts doubt on the argument/conclusion.

None of the other answer choices affect the author's argument, so (E) is definitely the best answer.
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