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VeritasKarishma
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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 does not state that ground-based telescopes are providing with the more light-gathering capacity required? How does one understand that?

VeritasKarishma GMATNinja


saby1410, aritrar4, mk96, enigma1504 - Missed some tags to this question. Here is a detailed analysis. Hope you find it useful.

Images from ground-based telescopes are invariably distorted by the Earth's atmosphere (in some way, whether winds, dust etc)

Orbiting space telescopes (above Earth's atmosphere) should provide superbly detailed images. Note the use of "should" - presumably because Earth's atmosphere does not interfere in their working. Does it actually happen, we don't know.

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

We need to weaken that ground based telescopes will become obsolete. They may have a disadvantage to space telescope but they may have some advantage too. Let's look at the options.

(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.

Irrelevant. There is no implication here that orbiting telescopes are far more expensive and difficult to launch. We are just told about this year's project is lagging while the project of ground telescope was on time and budget. We don't know what budget was allocated to each project.

(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.

So one kind of atmospheric distortion (which makes stars appear to twinkle) can be taken care of by placing the ground based telescopes on mountain summits. But does this take care of all atmospheric distortions? Does it make ground based telescopes relevant? We don't know. So will ground based telescopes become obsolete? Can't say.

(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.

So another kind of issue can be taken care of by carefully choosing location. So again, does this mean ground based telescope will stay relevant? Cannot say.

(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.

How we get the best "Earth based observations" is irrelevant.

(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.

A certain method which is used by astronomers to find data about stars requires telescope with more light gathering capacity than space telescopes. For at least this application then, ground telescopes will remain relevant. It is a method used by astronomers so it is reasonable to assume that ground based telescopes provide this facility. Else, how do the astronomers use detailed spectral analyses? After all, astronomers rely on it for determining the history of stars.
Hence it weakens that ground based telescopes will soon become obsolete for advanced astronomical research purposes.

Answer (E)
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VeritasKarishma ChiranjeevSingh GMATNinja


To reject D, can we also say that it talks about astronomical research, whereas the conclusion talks about advanced astronomical research.

Milky way galaxy may be a target of astronomical research but may not be of advanced astronomical research.

Thank you in advance!
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I see where you're coming from, but we don't know that the research mentioned in D is not advanced, so I wouldn't eliminate on those grounds. For all we know, it could be a target of research at all levels. In any case, we don't even need to get to the end of the sentence if we recognize that the best ground-based option could still be superseded if space-based observations are clear and all ground-based images are distorted. This answer is just comparing one ground-based option to others, so it has zero bearing on the argument.
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VeritasKarishma
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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 does not state that ground-based telescopes are providing with the more light-gathering capacity required? How does one understand that?

VeritasKarishma GMATNinja


saby1410, aritrar4, mk96, enigma1504 - Missed some tags to this question. Here is a detailed analysis. Hope you find it useful.

Images from ground-based telescopes are invariably distorted by the Earth's atmosphere (in some way, whether winds, dust etc)

Orbiting space telescopes (above Earth's atmosphere) should provide superbly detailed images. Note the use of "should" - presumably because Earth's atmosphere does not interfere in their working. Does it actually happen, we don't know.

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

We need to weaken that ground based telescopes will become obsolete. They may have a disadvantage to space telescope but they may have some advantage too. Let's look at the options.

(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.

Irrelevant. There is no implication here that orbiting telescopes are far more expensive and difficult to launch. We are just told about this year's project is lagging while the project of ground telescope was on time and budget. We don't know what budget was allocated to each project.

(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.

So one kind of atmospheric distortion (which makes stars appear to twinkle) can be taken care of by placing the ground based telescopes on mountain summits. But does this take care of all atmospheric distortions? Does it make ground based telescopes relevant? We don't know. So will ground based telescopes become obsolete? Can't say.

(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.

So another kind of issue can be taken care of by carefully choosing location. So again, does this mean ground based telescope will stay relevant? Cannot say.

(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.

How we get the best "Earth based observations" is irrelevant.

(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.

A certain method which is used by astronomers to find data about stars requires telescope with more light gathering capacity than space telescopes. For at least this application then, ground telescopes will remain relevant. It is a method used by astronomers so it is reasonable to assume that ground based telescopes provide this facility. Else, how do the astronomers use detailed spectral analyses? After all, astronomers rely on it for determining the history of stars.
Hence it weakens that ground based telescopes will soon become obsolete for advanced astronomical research purposes.

Answer (E)


VeritasKarishma ChiranjeevSingh GMATNinja


To reject D, can we also say that it talks about astronomical research, whereas the conclusion talks about advanced astronomical research.

Milky way galaxy may be a target of astronomical research but may not be of advanced astronomical research.

Thank you in advance!
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"astronomical research" of option (D) would possibly include "advanced astronomical research" too i.e. what is valid for astronomical research, is expected to be valid for basic as well as advanced.
Don't eliminate (D) based on this. So if (D) had given "advanced astronomical research", it wouldn't have been correct.

The problem is that (D) compares all earth based telescopes with each other and tells us which is the best. It does not compare ground based telescopes with orbiting telescopes. So anything (D) says is irrelevant.
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I can see why you took issue with (E). It clearly rules out space telescopes, but does it unequivocally state that Earth-based telescopes provide the needed "light-gathering capacity"? If we agree that a telescope is either Earth-based or Space-based, we could make such inference. It is a fact that astronomers rely on detailed spectral analyses for determining the chemical composition and evolutionary history of stars. If Space-based telescopes are unable to meet such need, we can assume that all the analyses so far (and for the foreseeable future) remain the domain of earth-based telescopes.

Regarding (D), it only says that "large-aperture telescopes located at high altitudes near the equator permit the best Earth-based observations of the center of the Milky Way Galaxy." What if any Space-based telescope permit even better observations? The key to rule (D) out is "earth-based".
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A very tricky question. But here's a cold truth to remember about the test: the GMAT loves 'binaries.'

It really seems like we only have two kinds of telescopes here: Earth based and space based. Answer E says that there's a certain method that astronomers *rely on* (note: present tense... It is happening *now*) to *do* (again, present tense) a certain kind of science. And space-based telescopes can't help in this kind of research, so that leaves Earth based telescopes to take up the task.

This is also a good 'four wrongs make a right' situation. Your answer choice of D says that there is a certain spot on Earth that gives the best view *from Earth* of the Milky Way. But the argument is that *all* Earth based telescopes (even those in the best location) will become obsolete (due to this atmospheric distortion that affects all earth-based telescopes). That there is a *best location* for Earth based telescopes does not weaken the argument that 'earth based telescopes will become obsolete' (in the same way that saying, "Someone gets fourth place!" doesn't weaken the argument that "Only the top three finishers in an olympic event get medals.")

B and C both talk about how choosing certain locations can help with some issues ground-based telescopes have--but not the thing the argument explicitly states affects *all* earth based telescopes. Answer A is just saying there's been some delays in space telescopes, which doesn't affect the argument that ground based will soon be obsolete.
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Option E . How is it correct?

It is highlighting the limitation Space Telescope but no where mentioned that the GBT has no such limitation or GBT is better than Space Telescope.

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Option E . How is it correct?

It is highlighting the limitation Space Telescope but no where mentioned that the GBT has no such limitation or GBT is better than Space Telescope.

Regards
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Hi Vibha6,

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.
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Option E . How is it correct?

It is highlighting the limitation Space Telescope but no where mentioned that the GBT has no such limitation or GBT is better than Space Telescope.

Regards
Hi Vibha6,

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.
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Hi AjiteshArun DmitryFarber - from E

Other than ground-based telescopes and space telescopes -- how do you know there is not a 3rd type of telescope (the argument never mentioned -- space telescopes and ground telescopes are the only two types of telescopes)

There could be under-ground / under-water telescopes (i dont believe an Underground telescope falls under the category of a 'ground-based telescope' -- an Underground /Under-water telescope are both well, under the ground)

-- Here is an article talking about under-ground telescopes here
-- Read about Underwater water telescopes, scanning the sky below : Based on this article, under ground telescopes are a thing
-- Here is another video talking about Russia deploying telescopes -- under the sea (lake baikal specifically - Watch here


Perhaps under water / under ground telescopes are being used for Detailed spectral analyses specifically- we can't say

Under-water / under-ground telescopes may also suffer the same issues as ground telescopes when it comes to distortion by the Earth's atmoshphere BUT Under-water / under-ground telescopes perhaps are being used for Detailed spectral analyses - we dont know !
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Hi DmitryFarber IanStewart avigutman - My question is on B specifically (not E)

In weaken question - we just have to cast doubt on the conclusion -

Wouldn't you agree - B DOES cast doubt on the conclusion, at least a bit ? Here is how

  • Ground space telescope at 'low altitudes' = 50 % clarity
  • Ground space telescopes at 'mountain summits' = 75 % clarity
  • Space telescopes = 99 % clarity


75 % clarity (when Ground space telescopes are placed 'mountain summits' ) is LOWER than 99 % clarity (when space telescopes are being used), so we are within the bounds of the premise.

But going from 50 % clarity to 75 % clarity itself , does cast doubt on the conclusion, a tiny bit - would it not ? Here's how.

Perhaps 50 % clarity -- Ground space telescopes at 'low altitude' are obselete specifically but the same Ground space telescopes at 'high altitude' [75 % clarity] is NOT OBSOLETE specifically

Thats my analysis on B as a weakener -- it 'could' weaken - a teeny bit

Thoughts ?
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jabhatta2

Wouldn't you agree - B DOES cast doubt on the conclusion, at least a bit ? Here is how
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Answer B only compares two types of ground-based telescopes -- it only tells us that some ground telescopes are better than others. It doesn't give us any reason to think that ground telescopes will be more useful, in some cases, than space telescopes, so it doesn't weaken the conclusion.

We already know as a factual premise from the stem that ground telescopes (whether placed on mountains or placed in canyons) are subject to distortion from the atmosphere, while space telescopes are not. Answer B just says that some ground telescopes experience less distortion than others, which still doesn't give us any reason to prefer ground telescopes to space telescopes, no matter where we put the ground telescope.
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Wouldn't you agree - B DOES cast doubt on the conclusion, at least a bit ? Here is how

Answer B only compares two types of ground-based telescopes -- it only tells us that some ground telescopes are better than others. It doesn't give us any reason to think that ground telescopes will be more useful, in some cases, than space telescopes, so it doesn't weaken the conclusion.

We already know as a factual premise from the stem that ground telescopes (whether placed on mountains or placed in canyons) are subject to distortion from the atmosphere, while space telescopes are not. Answer B just says that some ground telescopes experience less distortion than others, which still doesn't give us any reason to prefer ground telescopes to space telescopes, no matter where we put the ground telescope.
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Well said, IanStewart. jabhatta2 I would just add the following two points:
1. Please note the word "invariably" in the first sentence. This is a very important word. It implies that all ground-based telescopes suck. Answer choice (B) simply lets us know that the degree to which they suck depends on their altitude.
2. The author's reason for the conclusion is that while ground-based telescopes suck, orbiting telescopes provide superbly detailed images. How can the conclusion be weakened? We'd have to find something at which the former are better than the latter. Answer choice B doesn't do that.
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Images from ground-based telescopes are invariably distorted by the Updated on: 12 Jan 2022, 20:39
Originally posted by jabhatta2 on 12 Jan 2022, 20:33.
Last edited by jabhatta2 on 12 Jan 2022, 20:39, edited 2 times in total.
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Hi avigutman – I don’t know because if was to create the following analogy when it comes to option B
Quote:

- Blackberry phones invariably weigh heavier
- Average blackberry phone weight is 2 pounds
- Apple phones weigh 1.5 pounds

Conclusion : Blackberry phones are too heavy for folks who want light pockets

I would think this version of option B would be a weakener
Option B) When it comes to blackberry phones specifically – you can remove the physical keyboard from the phone completely – dropping the blackberry phone’s weight to 1.6 pounds

This will weaken because perhaps folks are okay with a 1.6 pound phone in their pockets BUT not a 2 pound phone in their pockets.
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Same thing with B i would think....this slight improvement in ground based telescope is enough to perhaps no longer consider it 'obsolete'
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AjiteshArun


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.

Other than ground-based telescopes and space telescopes -- how do you know there is not a 3rd type of telescope
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jabhatta2 you're right, we can't assume that space telescopes and ground-based telescopes are MECE.
But, remember: the correct answer needn't destroy the argument completely. It need only cast doubt on the conclusion. So, without knowing anything about telescopes or advanced astronomical research...
When you read answer choice E, does it cause you to reconsider the conclusion? Does this answer give you pause, and make you want to do a bit more research before you proceed with decommissioning all ground-based telescopes? It should.
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jabhatta2
Hi avigutman – I don’t know because if was to create the following analogy when it comes to option B
Quote:

- Blackberry phones invariably weigh heavier
- Average blackberry phone weight is 2 pounds
- Apple phones weigh 1.5 pounds

Conclusion : Blackberry phones are too heavy for folks who want light pockets

I would think this version of option B would be a weakener
Option B) When it comes to blackberry phones specifically – you can remove the physical keyboard from the phone completely – dropping the blackberry phone’s weight to 1.6 pounds

This will weaken because perhaps folks are okay with a 1.6 pound phone in their pockets BUT not a 2 pound phone in their pockets.
Show more

jabhatta2 I'm going to tweak your analogy a bit to make it more fitting. Let me know whether this helps you see the issue:

Blackberry phones are invariably heavy [distorted]. iPhones, however, are extremely light [superbly detailed images]. Therefore, Blackberry phones will soon become obsolete for folks who want light pockets.

(B) Some newer Blackberry phones aren't as heavy as the older Blackberry phones, which rip holes in pockets [[i]make stars appear to twinkle/i]]
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Hi AjiteshArun DmitryFarber - from E

Other than ground-based telescopes and space telescopes -- how do you know there is not a 3rd type of telescope (the argument never mentioned -- space telescopes and ground telescopes are the only two types of telescopes)

There could be under-ground / under-water telescopes (i dont believe an Underground telescope falls under the category of a 'ground-based telescope' -- an Underground /Under-water telescope are both well, under the ground)

-- Here is an article talking about under-ground telescopes here
-- Read about Underwater water telescopes, scanning the sky below : Based on this article, under ground telescopes are a thing
-- Here is another video talking about Russia deploying telescopes -- under the sea (lake baikal specifically - Watch here


Perhaps under water / under ground telescopes are being used for Detailed spectral analyses specifically- we can't say

Under-water / under-ground telescopes may also suffer the same issues as ground telescopes when it comes to distortion by the Earth's atmoshphere BUT Under-water / under-ground telescopes perhaps are being used for Detailed spectral analyses - we dont know !
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Hi jabhatta2,

Generally speaking, we shouldn't go looking for edge cases on the GMAT. Nor should we expect perfect answers. That said, that was a fascinating article you linked to, and I enjoyed reading it. However, the types of telescope this question is interested in are different. According to the question, their images are "invariably distorted by the Earth's atmosphere". There is no way for a terrestrial telescope to avoid the Earth's atmosphere, no matter where we put it. On top of a mountain, the surface of water, underground, underwater... the Earth's atmosphere will always get in the way. In other words, the question is a little like this:

1. If ~below the Earth's atmosphere, invariably distorted
2. Space telescopes are ~above the Earth's atmosphere, therefore not distorted

If something is distorted by the Earth's atmosphere for ground-based telescopes, surely it must also be distorted by the Earth's atmosphere for other types of telescopes, including, as you mentioned, underground telescopes. Therefore, we need something that space telescopes can't do with light, or we need some application that doesn't have anything to do with light, maybe exotic stuff like detecting neutrinos and dark matter, as mentioned in the article you linked to.

Therefore, if we don't like E, we need another option, one in which the GMAT itself tells us about such alternate technology/applications. But none of the options do that. Here's what we do have, option E:
kahipz
(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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There's no chance that a telescope will be able to gather light if it isn't exposed to light. If the atmosphere isn't good for light-gathering capacity, it's hard to argue that solid rock is. That means we're stuck with ground-based telescopes, and E is a pretty good answer, definitely the best of the 5 presented to us.
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Images from ground-based telescopes are invariably distorted by the 13 Jan 2022, 06:48
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jabhatta2
I don’t know because if was to create the following analogy when it comes to option B
Quote:

This will weaken because perhaps folks are okay with a 1.6 pound phone in their pockets BUT not a 2 pound phone in their pockets.

Same thing with B i would think....this slight improvement in ground based telescope is enough to perhaps no longer consider it 'obsolete'
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I think you're reading answer B differently from how I read it. You seem to be interpreting it to say "one thing astronomers haven't tried yet is putting telescopes on mountains, which will lead to less atmospheric distortion". But there's nothing in the passage that says mountain telescopes would be new -- the stem just says mountain telescopes are the best type of ground telescope. They're still ground telescopes, and the stem tells us ground telescopes are worse than space telescopes, if you want detailed images.

Read that way, your analogy becomes: Mulberry phones are significantly heavier than hPhones. Since consumers have a clear preference for lightweight phones, hPhone sales will soon overtake Mulberry phone sales.

If we wanted to cast doubt on that prediction, an answer choice like this would not be useful: the Mulberry X-model is 15% lighter than other Mulberry models. We already know from the stem that Mulberry phones are much heavier. It doesn't matter that some Mulberry phones are lighter than others.

Unless we learn that Mulberry phones will overcome their deficiency and become lighter, the only kind of answer that could be correct here is one that compares Mulberry phones and hPhones and gives us some reason consumers will buy the Mulberry phone despite the fact that it weighs more -- maybe it's cheaper, or takes better photos, or can work with the newest satellites or does something else that the hPhone can't.
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Images from ground-based telescopes are invariably distorted by the 13 Jan 2022, 09:58
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analogy for above ^^

avigutman -

premise : given pigs can fly
conclusion : pigs will fly at 10 kms/hr

(option F) pigs cannot fly

Option F is my analogy is not a weakener
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Images from ground-based telescopes are invariably distorted by the 13 Jan 2022, 10:43
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jabhatta2
analogy for above ^^

avigutman -

premise : given pigs can fly
conclusion : pigs will fly at 10 kms/hr

(option F) pigs cannot fly

Option F is my analogy is not a weakener
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Exactly. If this were an answer choice:
Ground based telescopes on mount Everest take superbly detailed images similar to what space telescopes take
it would cast doubt on the premise [Images from ground-based telescopes are invariably distorted by the Earth's atmosphere], not on the conclusion.

It seems to me, jabhatta2, that you found it difficult in this problem to take the premise at its word. You were told that images from all ground-based telescopes are inferior to orbiting telescopes, but you had a hard time believing that, or, for some reason, you felt it should matter whether all ground-based telescopes are equally terrible vs are terrible to varying degrees.
You clearly have a very creative mind, and you're curious about the world (I say this because of the research you did into underground telescopes), but those attributes can get you into trouble on CR, as they did here:
https://gmatclub.com/forum/for-a-trade- ... l#p2940214

Try to be more strict about sticking to the text, and avoid overthinking / telling yourself a story in your head.
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Images from ground-based telescopes are invariably distorted by the 15 Mar 2022, 03:49
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GMATNinja karishma In option E, is it safe to think that if space telescopes can't fulfill the purpose, only ground telescopes will solve it? No other types of telescopes? Or am I moving away from the argument thinking this way?
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Images from ground-based telescopes are invariably distorted by the 15 Mar 2022, 15:50
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avigutman
I got the impression based on the yellow highlights in option C , perhaps the red premise has a few exceptions.

Thus it created doubt in mind

Remember we are not looking for a 100 % wekener but something that just creates 'doubt'

thus i chose c
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