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09/26/2009 03:56:34 PM · #1
I have these astronomy questions that are a little confusing and any help would be great. Here's the first question: "Consider again the objects you ranked by distance in Part A, shown again here. Suppose each object emitted a light signal (such as a sudden spike in brightness) right now. Rank the objects from left to right based on the amount of time it would take for us here on Earth to see the light they emitted, from longest to shortest. (Not to scale.)"

The objects are the following: A star on the far side of Andromeda Galaxy, Star on near side of Andromeda, Star on Far side of Milky Way Galaxy, Star on near side of Milky Way Galaxy, Orion Nebula , Alpha Centauri, Pluto, The sun

I have already ranked them from furthest to nearest to the earth, so would they be the exact same for this question or would they all be equal because we have the capacity to see the light they emit no matter how far they are.
09/26/2009 04:04:09 PM · #2
Light travels at... the speed of light, which is pretty slow in a universal context. So, you won't see them all flash at once. The Andromeda galaxy for instance is a whopping 2.5 million light years away, so it will take 2.5 million years before you see the flash! The sun, on the other hand, is only 8 light-minutes away...
09/26/2009 04:04:31 PM · #3
It seems as though this is a homework question?

You seem to have figured most of it out. What exactly is the question? What have you rationalized up to this point? Are you trying to figure out how long a light pulse would take to get to the earth or the viewer's position?
09/26/2009 04:07:32 PM · #4
I have figured out these questions for the most part, but there are bits and pieces that make me unsure of my answer 100%

But from what I've gathered you wouldn't see the light emitted all at the same time, it would be dependent on how far the actual celestial object is from the earth
09/26/2009 04:12:19 PM · #5
Okay I got it correct, I stuck to what I initially thought.

This time, rank the objects (A-H) from left to right based on how much they have aged since they emitted the light we are seeing right now in the night sky, from greatest to least.

Isn't the same thing again :P because the furthest the object is the more older it has become
09/26/2009 04:35:25 PM · #6
yes

Looking at the night sky you see 2 stars (A and B)
Star A- 1 billion light years away, the light you are seeing is 1 billion years old, light being produced right now will not be seen here until 1 billion years from now.
Star B-2 billion light years away, the light you are seeing is 2 billion years old, light being produced right now will not be seen here until 2 billion years from now.

Message edited by author 2009-09-26 16:43:28.
09/26/2009 04:39:37 PM · #7
Alright it seems I got the astronomy questions all correct, but the last question I have gotten wrong several times it seems. I have to distinguish between Observation and Explanation, it says i got 2 incorrect out of 8 :S
09/26/2009 06:59:59 PM · #8
observation is what you see in the night sky, explanation is how you relay that to others.... :0


09/26/2009 09:04:52 PM · #9
"stars can shine brightly for billions of years" is that an observation or explanation
09/26/2009 09:14:34 PM · #10
Originally posted by cujee:

"stars can shine brightly for billions of years" is that an observation or explanation


LOL, You have to pick the language apart. Ask yourself if it is an explanation. It is not. It is simply a statement of fact, which is sometimes referred to as making an observation. SO, it is not something observed as in looked at, but observed as in spoken of.
09/26/2009 09:16:41 PM · #11
lol... it's weird cause I was able to sort out observation and explanation for non-astronomy subject matter, but whenever they use it in this context it seems to be more confusing. Not exactly sure why.
09/26/2009 09:22:54 PM · #12
Originally posted by kirbic:

Originally posted by cujee:

"stars can shine brightly for billions of years" is that an observation or explanation


LOL, You have to pick the language apart. Ask yourself if it is an explanation. It is not. It is simply a statement of fact, which is sometimes referred to as making an observation. SO, it is not something observed as in looked at, but observed as in spoken of.


I don't agree, we can at most observe for only a few decades, but we can enplane based on knowledge of what we know or guess at this point.
09/26/2009 09:36:53 PM · #13
Originally posted by alans_world:

I don't agree, we can at most observe for only a few decades, but we can enplane based on knowledge of what we know or guess at this point.


Well, yes, but the statement is not an explanation at all. It's merely an observation. Had it said "stars can shine brightly for billions of years because of the tremendous power output of nuclear fusion and the great mass of fuel available" that is an explanation. It provides a basis for understanding why stars may shine for billions of years.
09/26/2009 10:12:17 PM · #14
Originally posted by kirbic:

Originally posted by alans_world:

I don't agree, we can at most observe for only a few decades, but we can enplane based on knowledge of what we know or guess at this point.


Well, yes, but the statement is not an explanation at all. It's merely an observation. Had it said "stars can shine brightly for billions of years because of the tremendous power output of nuclear fusion and the great mass of fuel available" that is an explanation. It provides a basis for understanding why stars may shine for billions of years.


Still reading, school was a few years ago ;p, and I drifted into Uncertainty principle.I love learning!
09/26/2009 10:37:24 PM · #15
Depending on the size, they do shine for billions of years.

Fusion converts hydrogen to helium (our sun is doing this now). When Hydorgen is done then Helium will be fused to Lithium, with some left over Hydrogen, then Berillium (sp)...some carbon, Oxygen and on down the line of the periodic table !

Elements like gold and uranium, were formed when stars many times more massive that the Sun detonated in supernova explosions. All the Gold on Earth and all elements for that matter were made in the fusion reactors of stars.

I always wondered what Carl Sagan meant when he said "we are all made of stardust". I finally learned in Physics class.

Cool...er...hot !

Originally posted by kirbic:

Originally posted by alans_world:

I don't agree, we can at most observe for only a few decades, but we can enplane based on knowledge of what we know or guess at this point.


Well, yes, but the statement is not an explanation at all. It's merely an observation. Had it said "stars can shine brightly for billions of years because of the tremendous power output of nuclear fusion and the great mass of fuel available" that is an explanation. It provides a basis for understanding why stars may shine for billions of years.
09/27/2009 03:05:09 AM · #16
Questions are for Professors. Answers are for students.

Since I am a professor: What is the speed of light measured in furlongs per fortnight?
09/27/2009 03:12:16 AM · #17
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Threads are useless without photos here. : )

Message edited by author 2009-09-27 03:13:10.
09/27/2009 03:14:23 AM · #18
Originally posted by Dr.Confuser:

Questions are for Professors. Answers are for students.

Since I am a professor: What is the speed of light measured in furlongs per fortnight?

149,990,400,000 = (186,000 x 16 x 3600 x 14)
09/27/2009 03:23:44 AM · #19
Wow! I am in awe! At least I am in awe of your response time.

However, grasshopper, your answer is incorrect. According to Wolfram Alpha, the correct answer is 1.803 X 10 to the twelfth. 1.8 Tera Furlongs/Fortnight.

ETA: D&L, we need superscripts. How about a superscript button above forum posts?

Originally posted by GeneralE:

Originally posted by Dr.Confuser:

Questions are for Professors. Answers are for students.

Since I am a professor: What is the speed of light measured in furlongs per fortnight?

149,990,400,000 = (186,000 x 16 x 3600 x 14)


Message edited by author 2009-09-27 03:28:08.
09/27/2009 03:35:37 AM · #20
Bah .. a furlong is 1/8 mile, not 1/16 -- just cut my answer in half.
09/27/2009 03:45:25 AM · #21
Originally posted by Dr.Confuser:

Wow! I am in awe! At least I am in awe of your response time.

However, grasshopper, your answer is incorrect. According to Wolfram Alpha, the correct answer is 1.803 X 10 to the twelfth. 1.8 Tera Furlongs/Fortnight.

ETA: D&L, we need superscripts. How about a superscript button above forum posts?

Originally posted by GeneralE:

Originally posted by Dr.Confuser:

Questions are for Professors. Answers are for students.

Since I am a professor: What is the speed of light measured in furlongs per fortnight?

149,990,400,000 = (186,000 x 16 x 3600 x 14)


speed of light is dependent on medium it travels in.
//en.wikipedia.org/wiki/Speed_of_light

Another interesting thing is , theory of relativity. Which is based on the idea that speed of light in vacuum when looked from different reference frames should look the same (remains constant).. Which is crux of theory of relativity. Einstein was genius to realize this and use it.

ps:
i am no expert on theory of relativity. Just have little bit of idea about it.

09/27/2009 09:23:05 AM · #22
The light that we would see here, which originated at the points indicated in the OP, would be from locations in the universe that are no longer occupied by the objects from which the light originated, because everything is in motion. When we look up at night, we are looking into the past. To think that everything is moving directly away from us would be the same as thinking that the Earth is the center of the universe.
09/27/2009 10:36:40 AM · #23
Originally posted by MelonMusketeer:

The light that we would see here, which originated at the points indicated in the OP, would be from locations in the universe that are no longer occupied by the objects from which the light originated, because everything is in motion. When we look up at night, we are looking into the past. To think that everything is moving directly away from us would be the same as thinking that the Earth is the center of the universe.


The odd fact about a space which is expanding uniformly in all directions is that at any point within it, every other point seems to be receding, at a speed directly proportional to distance. In other words, it *does* seem like your personal point of reference is always the "center." Of course it's an illusion.
09/27/2009 10:38:32 AM · #24
Originally posted by GeneralE:

Bah .. a furlong is 1/8 mile, not 1/16 -- just cut my answer in half.


Actually, it still seems you missed a multiplier of 24 for hours per day... :-)
09/27/2009 11:01:19 AM · #25
Originally posted by kirbic:

Originally posted by GeneralE:

Bah .. a furlong is 1/8 mile, not 1/16 -- just cut my answer in half.


Actually, it still seems you missed a multiplier of 24 for hours per day... :-)

Dang, right -- I thought I had that in the seconds figure, but noooo ... ;-)

OK ... (186,000 x 3600 x 24 x 14) / 8 = 28,123,200,000 ... still doesn't seem to match the previously-cited answer ... :-(

Message edited by author 2009-09-27 11:10:08.
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