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# A photograph of the night sky was taken with the camera shutter open f

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A photograph of the night sky was taken with the camera shutter open f  [#permalink]

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25 Jul 2017, 09:25
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Which of the following most logically completes the argument?

A photograph of the night sky was taken with the camera shutter open for an extended period. The normal motion of stars across the sky caused the images of the stars in the photograph to appear as streaks. However, one bright spot was not streaked. Even if the spot were caused, as astronomers believe, by a celestial object, that object could still have been moving across the sky during the time the shutter was open, since __________.

(A) the spot was not the brightest object in the photograph

(B) the photograph contains many streaks that astronomers can identify as caused by noncelestial objects

(C) stars in the night sky do not appear to shift position relative to each other

(D) the spot could have been caused by an object that emitted a flash that lasted for only a fraction of the time that the camera shutter was open

(E) if the camera shutter had not been open for an extended period, it would have recorded substantially fewer celestial objects

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Re: A photograph of the night sky was taken with the camera shutter open f  [#permalink]

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25 Jul 2017, 09:31
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carcass wrote:
Which of the following most logically completes the argument?

A photograph of the night sky was taken with the camera shutter open for an extended period. The normal motion of stars across the sky caused the images of the stars in the photograph to appear as streaks. However, one bright spot was not streaked. Even if the spot were caused, as astronomers believe, by a celestial object, that object could still have been moving across the sky during the time the shutter was open, since __________.

A. the spot was not the brightest object in the photograph

B. the photograph contains many streaks that astronomers can identify as caused by noncelestial objects

C. stars in the night sky do not appear to shift position relative to each other

D. the spot could have been caused by an object that emitted a flash that lasted for only a fraction of the time that the camera shutter was open

E. if the camera shutter had not been open for an extended period, it would have recorded substantially fewer celestial objects

Straight D - the spot could have been caused by an object that emitted a flash that lasted for only a fraction of the time that the camera shutter was open
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Re: A photograph of the night sky was taken with the camera shutter open f  [#permalink]

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27 Jul 2017, 12:41
can someone explain why D is the answer? I chose B. Can someone explain why B is wrong?
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Re: A photograph of the night sky was taken with the camera shutter open f  [#permalink]

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27 Jul 2017, 22:26
B contradicts the previous sentence . It talks about non celestial object.
whereas Astronomers believe that it is celestial object and we have to provide reason why spot was captured instead of streak .

D completes the sentence perfectly
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Re: A photograph of the night sky was taken with the camera shutter open f  [#permalink]

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11 Aug 2017, 06:39
WHy C is wrong someone explain that
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Re: A photograph of the night sky was taken with the camera shutter open f  [#permalink]

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11 Aug 2017, 07:04
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If the shutter speed is slow, it can create an effect called “motion blur”, where moving objects appear blurred along the direction of the motion or appear as streaks as stars in this question. The celestial object not necessarily a star may have emitted a flash only for a fraction of the time when the shutter of the camera was open to capture light. Thus D logically completes the argument.
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Re: A photograph of the night sky was taken with the camera shutter open f  [#permalink]

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12 Aug 2017, 08:30
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A photograph of the night sky was taken with the camera shutter open for an extended period. The normal motion of stars across the sky caused the images of the stars in the photograph to appear as streaks. However, one bright spot was not streaked. Even if the spot were caused, as astronomers believe, by a celestial object, that object could still have been moving across the sky during the time the shutter was open, since __________.

Type - Explain

A. the spot was not the brightest object in the photograph - Incorrect - it does not explain the situation

B. the photograph contains many streaks that astronomers can identify as caused by noncelestial objects - Incorrect - it does not explain the situation

C. stars in the night sky do not appear to shift position relative to each other - Irrelevant

D. the spot could have been caused by an object that emitted a flash that lasted for only a fraction of the time that the camera shutter was open - Correct - although it was a celestial object , it did not cause a streak as it emitted light for a short duration

E. if the camera shutter had not been open for an extended period, it would have recorded substantially fewer celestial objects - Incorrect - it does not explain the situation

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Re: A photograph of the night sky was taken with the camera shutter open f  [#permalink]

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20 Sep 2017, 20:51
Which of the following most logically completes the argument?

A photograph of the night sky was taken with the camera shutter open for an extended period. The normal motion of stars across the sky caused the images of the stars in the photograph to appear as streaks. However, one bright spot was not streaked. Even if the spot were caused, as astronomers believe, by a celestial object, that object could still have been moving across the sky during the time the shutter was open, since __________.

A. the spot was not the brightest object in the photograph - Wrong: Out of scope

B. the photograph contains many streaks that astronomers can identify as caused by noncelestial objects -Wrong: Out of scope

C. stars in the night sky do not appear to shift position relative to each other - Wrong: Shell game ("relative to each other")

D. the spot could have been caused by an object that emitted a flash that lasted for only a fraction of the time that the camera shutter was open - Correct: when cause (flash) occurs, effect (spot) occurs

E. if the camera shutter had not been open for an extended period, it would have recorded substantially fewer celestial objects - Wrong: Out of scope
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Re: A photograph of the night sky was taken with the camera shutter open f  [#permalink]

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28 Sep 2017, 12:18
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haardiksharma wrote:
WHy C is wrong someone explain that

Think of how two cars moving on the highway going in the same direction appear not to shift position relative to each other, but in reality they are both in motion.

Similarly C is the trap answer for the pre-thinking that the celestial object which marks the bright spot might might be a star that does not shift position relative to the Earth. But instead of mentioning the Earth, C mentions stars relative to each other. Hence, it's incorrect as that's not what's happening in our scenario where the camera is on the Earth.
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Re: A photograph of the night sky was taken with the camera shutter open f  [#permalink]

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01 Oct 2017, 05:18
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gumnamibaba wrote:
haardiksharma wrote:
WHy C is wrong someone explain that

Think of how two cars moving on the highway going in the same direction appear not to shift position relative to each other, but in reality they are both in motion.

Similarly C is the trap answer for the pre-thinking that the celestial object which marks the bright spot might might be a star that does not shift position relative to the Earth. But instead of mentioning the Earth, C mentions stars relative to each other. Hence, it's incorrect as that's not what's happening in our scenario where the camera is on the Earth.

haardiksharma

I fell to the similar trap and chose answer choice C.

Adding to the above explanation, just ask yourself one question. In case, the star does not change its position relative to the other stars, then ,while other stars have appeared as streaks, why not the this star has appeared as streak?

But the argument says otherwise.

Hope I cleared your doubt.
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Re: A photograph of the night sky was taken with the camera shutter open f  [#permalink]

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01 Oct 2017, 06:00
The answer is D .
We are talking about the photograph taken by camera that opened for an extended period of time and the stars appear as streaks .
One spot was not streaked we have to solve this anomaly .
A does nothing to advance our case it just tries to get us lost in different direction.
B Again no difference .
C why will they shift their position they are all moving relative to each other.
D This is our answer it talks about the time during it was a streak .Now just think about it if the streak was over within a very short period as compared to the extended time it will be a spot .
E provides us no information how to resolve the anomaly.

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Re: A photograph of the night sky was taken with the camera shutter open f  [#permalink]

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20 Dec 2017, 21:49
C is a trap b/c C does not directly connect with the argument. In other words, there is a gap between the positions of stars and the flashes, or the spots in the photo. Furthermore, C does not help to explain why astronomers conclude that the object is still moving even though the camera does not spot any light.
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Re: A photograph of the night sky was taken with the camera shutter open f  [#permalink]

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06 Jan 2018, 05:05
A photograph of the night sky was taken with the camera shutter open for an extended period. The normal motion of stars across the sky caused the images of the stars in the photograph to appear as streaks. However, one bright spot was not streaked.

Even if the spot were caused, as astronomers believe, by a celestial object,

that object could still have been moving across the sky during the time the shutter was open, since __________.

Aren't we looking for an option which gives us an explanation that this celestial object was moving even though it created only a spot or flash of light?
Given the general pattern of the movement of the objects creating a streak of light.

How is D explaining this phenomena? It does not gives a plausibility of the movement of the object.

D. the spot could have been caused by an object that emitted a flash that lasted for only a fraction of the time that the camera shutter was open

@experts plz help. I am struggling to understand this.
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Re: A photograph of the night sky was taken with the camera shutter open f  [#permalink]

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06 Jan 2018, 22:57
Leo8 wrote:
A photograph of the night sky was taken with the camera shutter open for an extended period. The normal motion of stars across the sky caused the images of the stars in the photograph to appear as streaks. However, one bright spot was not streaked.

Even if the spot were caused, as astronomers believe, by a celestial object,

that object could still have been moving across the sky during the time the shutter was open, since __________.

Aren't we looking for an option which gives us an explanation that this celestial object was moving even though it created only a spot or flash of light?
Given the general pattern of the movement of the objects creating a streak of light.

How is D explaining this phenomena? It does not gives a plausibility of the movement of the object.

D. the spot could have been caused by an object that emitted a flash that lasted for only a fraction of the time that the camera shutter was open

@experts plz help. I am struggling to understand this.

It is b/c D explains why "one bright spot was not streaked". In other word, D states that the flash is still there, so the conclusion is still true.
Also, D is the only option that connects directly with the argument. Hope it helps.
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Re: A photograph of the night sky was taken with the camera shutter open f  [#permalink]

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09 Jan 2018, 16:17
I am also struggling to understand this.

D is the perfect alternative explanation for the fact that the point wasn´t streak BUT I don´t understand why it´s the correct answer when the argument kind of asks for an explanation of why the celestial object could still have been moving across the sky. It says "that object could still have been moving across the sky during the time the shutter was open, since __________. " Doesn´t that "since" refers to "why it could still have been moving across the sky"?

What am I geting wrong in here? I find no way to interpret the last part of the argument in the way that it encourages me to find an alternative explanation for how the spot could have been created rather than find a corroboration that if the object had been a celestial object it would have still been moving and so the spot couldn´t have been created by a celestial object.

I am going to need some little support in here. I´m having horrible headaches with this question.

Thanks for any replies

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Re: A photograph of the night sky was taken with the camera shutter open f  [#permalink]

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23 Feb 2018, 08:36
RooIgle wrote:
I am also struggling to understand this.

D is the perfect alternative explanation for the fact that the point wasn´t streak BUT I don´t understand why it´s the correct answer when the argument kind of asks for an explanation of why the celestial object could still have been moving across the sky. It says "that object could still have been moving across the sky during the time the shutter was open, since __________. " Doesn´t that "since" refers to "why it could still have been moving across the sky"?

What am I geting wrong in here? I find no way to interpret the last part of the argument in the way that it encourages me to find an alternative explanation for how the spot could have been created rather than find a corroboration that if the object had been a celestial object it would have still been moving and so the spot couldn´t have been created by a celestial object.

I am going to need some little support in here. I´m having horrible headaches with this question.

-

The above info says that: motion of stars ... caused the images of them in photo to appear as streaks. The bright spot was not streaked, but it could still have been moving...during the time the shutter was open. So we're looking for an explanation for that whole thing, not just the part: "why it could still have been moving...".
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Re: A photograph of the night sky was taken with the camera shutter open f  [#permalink]

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11 Jun 2018, 00:17
haardiksharma wrote:
WHy C is wrong someone explain that

Two people are walking together at the same speed and the cameraman tries to make a short video of these two. To the cameraman, would they appear to be at rest or in motion?
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Re: A photograph of the night sky was taken with the camera shutter open f  [#permalink]

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27 Sep 2018, 00:48
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Which of the following most logically completes the argument?

Quote:
A photograph of the night sky was taken with the camera shutter open for an extended period. The normal motion of stars across the sky caused the images of the stars in the photograph to appear as streaks. However, one bright spot was not streaked. Even if the spot were caused, as astronomers believe, by a celestial object, that object could still have been moving across the sky during the time the shutter was open, since __________.
Argument Analysis:
1. A photograph of the night sky taken with camera shutter open for an extended period.
2. The normal motion of stars across the sky caused the images of the stars in the photograph to appear as streaks (Long thin line...) Which means that the camera shutter kept capturing the light that was available during the whole duration of the open shutter, or may be the longer the light was available, the longer the streak became.
3. Now author brings the contrast here and says that "One Bright spot wasn't a streak"
4. Even though the astronomer believe that the spot was because of the celestial object, and that object could still have been moving across the sky during the time the shutter was open.(Then what makes that celestial object different form other stars, which appeared as streaks. Why didn't this celestial body didn't appear as streak?)
We need to account for some difference between both of these celestial bodies to give a reason for the same...
Quote:
(A) the spot was not the brightest object in the photograph
Even if it wasn't the brightest object in the photograph, if it had the normal motion of the star in the sky and a constant light, it should have appeared as a streak and not as a spot. This option doesn't account for the difference.
Quote:
(B) the photograph contains many streaks that astronomers can identify as caused by noncelestial objects
1. Non celestial objects aren't the matter of concern here in the argument
2. Also we aren't concerned about the streaks formed by the non-celestial/celestial objects, but rather with the spot in the photograph.
Quote:
(C) stars in the night sky do not appear to shift position relative to each other
This no where makes any connection with the overall argument. Weather stars appear to shift portion to each other or not is not of concerns here. If the stars shift positions to each other then the relative streaks shall be seen as changing positions relative to each other. Doesn't addresses anything with the argument.
Quote:
(D) the spot could have been caused by an object that emitted a flash that lasted for only a fraction of the time that the camera shutter was open
This absolutely seems to hit the target. If there is an object that appeared for a fraction of time that the camera shutter was open, the camera made the image for only that particular time and for the rest of the time the camera saw dark image in that place, here only a spot got formed in the image. This explains the spot formation clearly. Let's keep D
Quote:
(E) if the camera shutter had not been open for an extended period, it would have recorded substantially fewer celestial objects
Would it record fewer or many celestial objects isn't something that deals in anyway with our concern of the bright spot mentioned in the argument. Goes Out.
D is the best option available...
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A photograph of the night sky was taken with the camera shutter open f  [#permalink]

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22 Oct 2018, 03:08
Quote:
Which of the following most logically completes the argument?

A photograph of the night sky was taken with the camera shutter open for an extended period. The normal motion of stars across the sky caused the images of the stars in the photograph to appear as streaks. However, one bright spot was not streaked. Even if the spot were caused, as astronomers believe, by a celestial object, that object could still have been moving across the sky during the time the shutter was open, since __________.

Argument Construction

Situation In a photograph of the night sky taken with the camera shutter open for an extended period, the images of stars appeared as streaks because of the stars' normal motion across the sky, but one bright spot was not streaked.

Reasoning What would most strongly suggest that a celestial object moving across the sky could have caused the spot? An object moving across the sky that was bright throughout the time the camera shutter was open should have appeared as a streak in the photograph, just as the stars did. But if the moving object was bright for only a very brief moment, and thus not for an extended time while the camera shutter was open, the object's movement may not have been captured in the photograph, and thus would appear in the photograph as an unstreaked bright spot.

Quote:
(A) the spot was not the brightest object in the photograph

The argument is not about how bright the spot was compared to other objects in the photograph.

Quote:
(B) the photograph contains many streaks that astronomers can identify as caused by noncelestial objects

Streaks caused by noncelestial objects such as satellites or airplanes do not explain how only one of many celestial objects moving across the sky could have produced the unstreaked spot.

Quote:
(C) stars in the night sky do not appear to shift position relative to each other

The passage indicates that the stars were shifting position relative to the camera, not relative to one another. In any case, this observation does not help to explain how a celestial object that may not have been a star but that was moving across the sky could have produced the unstreaked spot in the photograph.

Quote:
(D) the spot could have been caused by an object that emitted a flash that lasted for only a fraction of the time that the camera shutter was open

Option D is Correct. As explained above, a moving celestial object that only produced a momentary flash of light would produce an unstreaked bright spot in the photograph.

Quote:
(E) if the camera shutter had not been open for an extended period, it would have recorded substantially fewer celestial objects

This may be true, given that fewer celestial objects might have moved into the camera's range of view if the camera shutter had not been open as long. But it does not provide any evidence that a moving celestial object could have produced the unstreaked spot.
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A photograph of the night sky was taken with the camera shutter open f  [#permalink]

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01 Dec 2018, 22:54
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I got this incorrect by selecting the trap answer C, which suggests that the stars were shifting relative to each other, not the camera.
I overlooked (d) because of the excessive verbiage as well.

Conclusion: Even if the object were a celestial object, that object could still have been moving....
Why? (Premise):.......................

Now look at this photo https://pictures.digitalrev.com/image/upload/w_1920,c_fill/v1432523673/biowgedin4hvphiszndp.jpg

Notice the streaked lights and unstreaked lights. The objects that have no streaks are not moving or are moving very slowly (look at the cars parked in traffic).
Here's the logic behind exposure photograph: moving objects with consistent lighting will streak in photos, but stationary objects (even objects with consistent lighting) will not streak.
So applying this logic to our answers, it's easier to see how (d) is the answer.

The gist of (d): an object could still be moving but since it's not a star, it may not be emitting light the entire time.

So let's complete the argument:
Conclusion: Even if the object were a celestial object, that object could still have been moving....
Why? (Premise):...since that object may not be emitting light consistently like stars do
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