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Thread: Some questions on astrophysics...

  1. #1 Some questions on astrophysics... 
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    Imagine that you are surveying the sky, and take images of two galaxies. Galaxy A looks twice as wide as Galaxy B - i.e. it subtends twice the angle as viewed from the Earth, with an apparent radius of twice as many pixels.
    Which one of these statements cannot be true?

    If the two galaxies are really the same size, B must be twice as far away as A.

    If the two galaxies are at the same distance from the Earth, B must be half the size of A

    .If galaxy B is really twice as large as A, it must be four times further away.

    If galaxy A is really four times as big as galaxy B, it must be twice as far away.

    If galaxy B is really half the size of galaxy A, it must be twice as far away.


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    If this is a homework question we can't give answers, but it might help if you draw a picture (just using a dot for Earth and two lines or circles for the two galaxies).


     

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    If Galaxy A has twice the apparent angular diameter of Galaxy B, then

    Quote Originally Posted by Mayflow View Post

    If galaxy B is really half the size of galaxy A, it must be twice as far away.
    This cannot be true.

    If galaxy B is really half the size of galaxy A, and Galaxy A looks to be twice as wide as Galaxy B as you initially said, then they must be at the same distance.

    EDIT:
    Oops, I hope this isn't homework. I don't recall you saying you were studying astrophysics.
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    I already know the answer. Tell me what you think, and I will tell you if it is correct. Remember one thing. Electromagnetic waves lose intensity with the square of the inverse of the distance.

    Inverse-square law - Wikipedia, the free encyclopedia
     

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    Oh, you are testing us?!

    Your last comment has no bearing on your original question, as you didn't specify anything about apparent luminosity, only size.

    If two objects have the same absolute luminosity, but one object looks to be dimmer than the other, then the dimmer object is further away.

    But the inverse square law has no effect on the apparent size of objects, it only affects their luminosity.
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    As a follow on, have a look at the following webpage, and note the section on Angular Diameter Distance:

    "In an expanding universe, we see the galaxies near the edge of the visible universe when they were very young nearly 14 billion years ago because it has taken the light nearly 14 billion years to reach us. However, the galaxies were not only young but they were also at that time much closer to us.

    The faintest galaxies visible with the Hubble Space Telescope were only a few billion light years from us when they emitted their light. This means that very distant galaxies look much larger than you would normally expect as if they were only about 2 or 3 billion light years from us (although they are also very very faint - see Luminosity Distance).

    Angular Diameter Distance is a good indication (especially in a flat universe like ours) of how near the galaxy was to us when it emitted the light that we now see."

    The Distance Scale of the Universe
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    While the answer to the original question was correct (as far as I know), I am less convinced about the flat Universe theory, and there is something I don't think right about how close the Galaxies were to Us at first, because I don't see anything that says the Earth even existed when a first Galaxy existed. Also, what Galaxy? There appear to be countless of them.
     

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    Quote Originally Posted by Mayflow View Post


    Imagine that you are surveying the sky, and take images of two galaxies. Galaxy A looks twice as wide as Galaxy B - i.e. it subtends twice the angle as viewed from the Earth, with an apparent radius of twice as many pixels.
    Let the be the subtended angle, be the radius and be the distance between the observer and the center of the galaxy. Elementary geometry teaches you that :

    , so your starting sentence "Galaxy A looks twice as wide as Galaxy B - i.e. it subtends twice the angle as viewed from the Earth, with an apparent radius of twice as many pixels" can NEVER be correct. So, your premise is DOA and everything that follows is garbage. You can stop trolling now.
     

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    Whilst the Earth didn't exist when galaxies first formed, this region in the universe did exist, and the light from those galaxies (which were originally quite close but are now much more distant) was heading in this direction. The reason that light took so long to reach this place is because the universe was expanding so fast, early on, and the space between that light and "here" was increasing faster than the light could cross it. By the time that light eventually reached here, the Earth had formed and we had evolved.

    As for "what galaxies", well our view out into the universe is a slice backwards through time, all the way back to when galaxies first formed and beyond. We see different galaxies whose light was emitted at different times, at different distances.

    A post I made a while back explains this in far more detail. Have a look here. It contains a diagram with my explanation of how our view out into the universe works, and the diagram includes a telescope view of how galaxies of the same actual size would have different apparent sizes due to the expansion, which I can explain in more detail if you want.
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    Quote Originally Posted by xyzt View Post
    , so your starting sentence "Galaxy A looks twice as wide as Galaxy B - i.e. it subtends twice the angle as viewed from the Earth, with an apparent radius of twice as many pixels" can NEVER be correct. So, your premise is DOA and everything that follows is garbage. You can stop trolling now.
    I didn't get that. A galaxy with an apparent angular diameter twice as wide as another will subtend twice the angle, won't it? Doesn't an object with an apparent angular diameter of 10 degrees look twice as wide as an object with an apparent angular diameter of 5 degrees?
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    Quote Originally Posted by SpeedFreek View Post
    Quote Originally Posted by xyzt View Post
    , so your starting sentence "Galaxy A looks twice as wide as Galaxy B - i.e. it subtends twice the angle as viewed from the Earth, with an apparent radius of twice as many pixels" can NEVER be correct. So, your premise is DOA and everything that follows is garbage. You can stop trolling now.
    I didn't get that. A galaxy with an apparent angular diameter twice as wide as another will subtend twice the angle, won't it?
    Elementary geometry says "no", the dependency between the subtended arc and the subtended radius (diameter) is NOT linear. :-)
     

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    Most science I have been studying is saying that space is expanding faster now than ever before and shows no signs of slowing down.


    Dark Energy, Dark Matter - NASA Science - which is my new subject - and we are talking about NASA and such here and some pretty intelligent people. The farther things are away from each other, the higher the red shift, which indicate the expansion is speeding up, not slowing down.
     

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    xyzt, if we imagine our view of the sky, from horizon to horizon, takes up 180 degrees, then wouldn't an object that spanned 90 degrees of our view look half the width of an object that spanned the whole 180 degrees? Apart from a mathematical education, what am I missing here? Can you make it simple for me?
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    Quote Originally Posted by SpeedFreek View Post
    xyzt, if we imagine our view from of the sky, from horizon to horizon, takes up 180 degrees, then wouldn't an object that spanned 90 degrees of our view look half the width of an object that spanned the whole 180 degrees? Apart from a mathematical education, what am I missing here? Can you make it simple for me?
    Sure: is NOT , i.e. the dependency is NOT linear. Makes sense?
     

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    Quote Originally Posted by Mayflow View Post
    Most science I have been studying is saying that space is expanding faster now than ever before and shows no signs of slowing down.


    Dark Energy, Dark Matter - NASA Science - which is my new subject - and we are talking about NASA and such here and some pretty intelligent people. The farther things are away from each other, the higher the red shift, which indicate the expansion is speeding up, not slowing down.
    Indeed. Feel free to ask about it if you have any questions.
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    Speedfreak, no point I think to argue. Here is why you were correct... EXPLANATIONIf galaxy B were really half the size of galaxy A, then they must be at the same distance. If it were twice as far away it would appear four times smaller (two times smaller because of distance and another factor of two from its size).
     

  18. #17  
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    Quote Originally Posted by xyzt View Post
    Quote Originally Posted by SpeedFreek View Post
    xyzt, if we imagine our view from of the sky, from horizon to horizon, takes up 180 degrees, then wouldn't an object that spanned 90 degrees of our view look half the width of an object that spanned the whole 180 degrees? Apart from a mathematical education, what am I missing here? Can you make it simple for me?
    Sure: is NOT , i.e. the dependency is NOT linear. Makes sense?
    Like I said, maths is not my strong point.

    But in this article by Phil Plait, he says the moon is about 0.5 degrees across whilst Andromeda is more than 3 degrees across, so Andromeda looks around 6 times bigger. Now that makes sense to me.

    So is this a question of terminology again? Is subtend the wrong term for what Phil is describing?

    Moon and Andromeda: Relative size in the sky.
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    Quote Originally Posted by SpeedFreek View Post
    Quote Originally Posted by xyzt View Post
    Quote Originally Posted by SpeedFreek View Post
    xyzt, if we imagine our view from of the sky, from horizon to horizon, takes up 180 degrees, then wouldn't an object that spanned 90 degrees of our view look half the width of an object that spanned the whole 180 degrees? Apart from a mathematical education, what am I missing here? Can you make it simple for me?
    Sure: is NOT , i.e. the dependency is NOT linear. Makes sense?
    Like I said, maths is not my strong point.

    But in this article by Phil Plait, he says the moon is about 0.5 degrees across whilst Andromeda is more than 3 degrees across, so Andromeda looks around 6 times bigger. Now that makes sense to me.

    So is this a question of terminology again? Is subtend the wrong term for what Phil is describing?

    Moon and Andromeda: Relative size in the sky.
    For SMALL angles , so Phil Platt is APPROXIMATELY correct for SMALL angles ONLY. To do physics, you need to have a strong math background.
     

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    Ok, getting around to Luminsosity

    Imagine that you have just discovered two stars, which you believe to have the same luminosities. Star A has a measured flux four times greater than Star B.
    Which one of the following statements is correct?

    Star A is twice as far away as Star B.
    Star B is twice as far away as Star A
    Star A is four times as far away as Star B
    Star B is four times as far away as Star A
    None of the other answers is correct
     

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    Quote Originally Posted by xyzt View Post
    For SMALL angles , so Phil Platt is APPROXIMATELY correct for SMALL angles ONLY. To do physics, you need to have a strong math background.
    Yes, which is why I am not a physicist!

    But I cannot see why an object with a width that spreads across half the sky (90 degrees) doesn't look half the width (have half the apparent angular diameter) of an object with a width that spreads across the whole sky (180 degrees). It would seem at first blush to be trivially obvious to me. Sorry if I am frustrating you here. I haven't dealt with sines cosines or tangents for over 30 years.

    So, does something with an apparent angular diameter of 90 degrees look less than, or more than half the width of something with an apparent angular diameter of 180 degrees?
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    Quote Originally Posted by Mayflow View Post

    Star B is twice as far away as Star A
    For the luminosity question, this one is the correct statement.
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    Correct again. See, you do well in this. I have no idea however of xyzt is on about. Must be on about another topic. Hope it returns there.
     

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    Quote Originally Posted by SpeedFreek View Post

    So, does something with an apparent angular diameter of 90 degrees look less than, or more than half the width of something with an apparent angular diameter of 180 degrees?
    Your question is so ill formed that it makes no sense. There is no such thing as "angular diameter".
     

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    Quote Originally Posted by Mayflow View Post
    I have no idea however of xyzt is on about.
    I'm about you posting nonsense and pretending that it is science, as you always do.
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    Quote Originally Posted by xyzt View Post
    Quote Originally Posted by SpeedFreek View Post

    So, does something with an apparent angular diameter of 90 degrees look less than, or more than half the width of something with an apparent angular diameter of 180 degrees?
    Your question is so ill formed that it makes no sense. There is no such thing as "angular diameter".
    Oh, yes there is. It is how astronomers measure the size of objects in the sky, i.e. the subject of this discussion.

    Angular diameter - Wikipedia, the free encyclopedia

    Anyway, I think I now understand what you were saying. Sorry for being so geometrically dense, xyzt, and thank you for being so gentle! If in doubt, I should draw myself a diagram!

    The objects we are looking at in the sky are not following large curves. If we imagine two long straight rods sitting up in the sky across our view, where Rod A subtends 40 degrees whilst Rod B subtends 80 degrees, then Rod B looks less than twice the width of rod A, because they are not arcs!

    In the diagram I drew below, the red angle is 40 degrees and the blue angle is 80 degrees, but the blue horizontal line is less than twice the length of the red horizontal line. Got it.



    And in cosmology, the angular diameter - redshift relationship is used as an important distance measure (see the section halfway down the following webpage):

    http://www.astr.ua.edu/keel/galaxies/obscosmo.html
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    Quote Originally Posted by SpeedFreek View Post
    Quote Originally Posted by xyzt View Post
    Quote Originally Posted by SpeedFreek View Post

    So, does something with an apparent angular diameter of 90 degrees look less than, or more than half the width of something with an apparent angular diameter of 180 degrees?
    Your question is so ill formed that it makes no sense. There is no such thing as "angular diameter".
    Oh, yes there is. It is how astronomers measure the size of objects in the sky, i.e. the subject of this discussion.

    Angular diameter - Wikipedia, the free encyclopedia

    Anyway, I think I now understand what you were saying. Sorry for being so geometrically dense, xyzt, and thank you for being so gentle! If in doubt, I should draw myself a diagram!
    ...and follow the simple math :-)
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    One way to measure distances is if you know the size of an object. If you can then measure its apparent angular size, you can work out the distance:


    Given the geometry above, and if Dr, (almost always the case in astronomy), then
    r=θD
    as long as θ is measured in radians (a radian is 180/π degrees).
    Angles in astrophysics are often so small that even a degree is too large a unit to be convenient. Typically they use arcminutes (one arcminute is 1/60 of a degree) and arcseconds (one arcsecond = 1/60 of an arcminute = 1/3600 of a degree).
     

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    Quote Originally Posted by Mayflow View Post
    One way to measure distances is if you know the size of an object. If you can then measure its apparent angular size, you can work out the distance:


    Given the geometry above, and if Dr, (almost always the case in astronomy), then
    r=θD
    as long as θ is measured in radians (a radian is 180/π degrees).
    Angles in astrophysics are often so small that even a degree is too large a unit to be convenient. Typically they use arcminutes (one arcminute is 1/60 of a degree) and arcseconds (one arcsecond = 1/60 of an arcminute = 1/3600 of a degree).

    Sure, but (back in a normal type size) why are you reciting this? I can't see what your point is, in this thread. Can you clarify?
     

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    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by Mayflow View Post
    One way to measure distances is if you know the size of an object. If you can then measure its apparent angular size, you can work out the distance:


    Given the geometry above, and if Dr, (almost always the case in astronomy), then
    r=θD
    as long as θ is measured in radians (a radian is 180/π degrees).
    Angles in astrophysics are often so small that even a degree is too large a unit to be convenient. Typically they use arcminutes (one arcminute is 1/60 of a degree) and arcseconds (one arcsecond = 1/60 of an arcminute = 1/3600 of a degree).

    Sure, but (back in a normal type size) why are you reciting this? I can't see what your point is, in this thread. Can you clarify?
    Well, the first question I posed was about d i s t a n c e and size. You will have to clarify your question about my point(s) in this thread as to whether you wonder why the large type thingy seemed to me to belong here, or why to make the thread over all.
     

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    Mayflow, are you letting your bot make some of your posts? IF so, stop immediately or face suspension. If not, please try and make more sense.
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

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  32. #31  
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    Quote Originally Posted by Mayflow View Post
    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by Mayflow View Post
    One way to measure distances is if you know the size of an object. If you can then measure its apparent angular size, you can work out the distance:


    Given the geometry above, and if Dr, (almost always the case in astronomy), then
    r=θD
    as long as θ is measured in radians (a radian is 180/π degrees).
    Angles in astrophysics are often so small that even a degree is too large a unit to be convenient. Typically they use arcminutes (one arcminute is 1/60 of a degree) and arcseconds (one arcsecond = 1/60 of an arcminute = 1/3600 of a degree).

    Sure, but (back in a normal type size) why are you reciting this? I can't see what your point is, in this thread. Can you clarify?
    Well, the first question I posed was about d i s t a n c e and size. You will have to clarify your question about my point(s) in this thread as to whether you wonder why the large type thingy seemed to me to belong here, or why to make the thread over all.
    The first question you posed was one you told us you already knew the answer to. So what was that in aid of?

    Since then I have struggled to see what you are getting at.

    And now you are just being tiresome by deliberately pretending to misunderstand my query.

    I have tried to treat you with respect but it is getting harder and harder in the face of what looks like silly provocation.
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    Quote Originally Posted by Mayflow View Post
    The farther things are away from each other, the higher the red shift, which indicate the expansion is speeding up, not slowing down.
    Careful. If the rate (*) of expansion were constant then there would be a linear relationship between distance and red-shift (this was one of the first pieces of evidence, bit not the strongest, for the big bang theory). Accelerating expansion means that the more distant galaxies have slightly less red-shift than expected.

    (*) note that expansion is not a speed.
    Without wishing to overstate my case, everything in the observable universe definitely has its origins in Northamptonshire -- Alan Moore
     

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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by Mayflow View Post
    The farther things are away from each other, the higher the red shift, which indicate the expansion is speeding up, not slowing down.
    Careful. If the rate (*) of expansion were constant then there would be a linear relationship between distance and red-shift (this was one of the first pieces of evidence, bit not the strongest, for the big bang theory). Accelerating expansion means that the more distant galaxies have slightly less red-shift than expected.

    (*) note that expansion is not a speed.
    Expansion of space it seems. What seems to be is that the farther away the galaxies are from us, the more the red shift and the faster they are moving away. I don't know if there is a constant in this or not. http://science.nasa.gov/media/medial.../image_preview
     

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    Quote Originally Posted by Mayflow View Post
    I don't know if there is a constant in this or not.
    It was assumed to be constant until Saul Perlmutter, Brian Schmidt and Adam Riess made their Nobel-prize winning discovery.
    Dark Energy Wins Nobel Prize in Physics | Popular Science
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    Brian Schmidt is one of my course instructors! I didn't know about the Nobel prize, too cool! I'll see if I can post a vid.

    https://courses.edx.org/courses/ANUx...4fba8be7c3542/
    Last edited by Mayflow; April 12th, 2014 at 06:36 AM.
     

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    Did that link even sort of work for any of you? If not, I see he has lots of stuff of youtube. I know at least one other on this forum is also taking this course put on by the National University of Australia - it's a really tough course, but certainly fun.
     

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    Quote Originally Posted by Mayflow View Post
    Did that link even sort of work for any of you? If not, I see he has lots of stuff of youtube. I know at least one other on this forum is also taking this course put on by the National University of Australia - it's a really tough course, but certainly fun.
    No. It asked me to log in to my Ed Ex account.

    Please, what point are you trying to make?

    Or are you just telling us what you are learning, or something?

    I'm totally baffled by the purpose of this thread.
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    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by Mayflow View Post
    Did that link even sort of work for any of you? If not, I see he has lots of stuff of youtube. I know at least one other on this forum is also taking this course put on by the National University of Australia - it's a really tough course, but certainly fun.
    No. It asked me to log in to my Ed Ex account.

    Yeh, that was what I thought it may do for others.

    Please, what point are you trying to make? No points to make, just discussing.

    Or are you just telling us what you are learning, or something? Yep

    I'm totally baffled by the purpose of this thread.
    Thanks, I didn't know if you were baffled by that one post I made about distance and angles and size, or about the whole thread. It would have been much nicer for you to say in the first place than to decide to call me names, though.

    The purpose of the thread is to think and discover and share and learn.

    I didn't realize Brian had won a Nobel prize for his work, but I do know he is one heck of a bright guy.

    Also Paul,
    Paul Francis' Web Page

    I
    come here to share and talk about stuff like this, not for people to call me bad names.
     

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    Quote Originally Posted by Mayflow View Post
    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by Mayflow View Post
    Did that link even sort of work for any of you? If not, I see he has lots of stuff of youtube. I know at least one other on this forum is also taking this course put on by the National University of Australia - it's a really tough course, but certainly fun.
    No. It asked me to log in to my Ed Ex account.

    Yeh, that was what I thought it may do for others.

    Please, what point are you trying to make? No points to make, just discussing.

    Or are you just telling us what you are learning, or something? Yep

    I'm totally baffled by the purpose of this thread.
    Thanks, I didn't know if you were baffled by that one post I made about distance and angles and size, or about the whole thread. It would have been much nicer for you to say in the first place than to decide to call me names, though.

    The purpose of the thread is to think and discover and share and learn.

    I didn't realize Brian had won a Nobel prize for his work, but I do know he is one heck of a bright guy.

    Also Paul,
    Paul Francis' Web Page

    I
    come here to share and talk about stuff like this, not for people to call me bad names.
    I'm not aware of having called you names. I generally try to avoid this, unless I've totally had it with some terminal case of idiocy. What names were these, please and in what posts?

    But anyway, thanks for the clarification about the thread. I do think it is confusing though, if a person titles a thread "some questions about astrophysics" , but then has no genuine questions, only ones to which the poster already has the answer.

    But now we've cleared up that misunderstanding, I'm more than willing to engage you on photons and atomic spectra, if you are interested and can formulate questions or topic clearly enough for me to understand them.
     

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    Your words exchemist, not mine = "And now you are just being tiresome by deliberately pretending to misunderstand my query.

    I have tried to treat you with respect but it is getting harder and harder in the face of what looks like silly provocation."

    The questions are ones that have been asked by a guy who won the Nobel prize in physics in 2011, for gosh sakes!, and sorry but at present, I don't see any help you can be to my studies.
    Last edited by Mayflow; April 12th, 2014 at 04:26 PM.
     

  42. #41  
    Anti-Crank AlexG's Avatar
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    Trolling and flaming.
    Its the way nature is!
    If you dont like it, go somewhere else....
    To another universe, where the rules are simpler
    Philosophically more pleasing, more psychologically easy
    Prof Richard Feynman (1979) .....

    Das ist nicht nur nicht richtig, es ist nicht einmal falsch!"
     

  43. #42  
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    Quote Originally Posted by Mayflow View Post
    Your words exchemist, not mine = And now you are just being tiresome by deliberately pretending to misunderstand my query.

    I have tried to treat you with respect but it is getting harder and harder in the face of what looks like silly provocation.
    Ah but saying you are "being tiresome" is not calling you names, it is describing your behaviour. Calling you names would be saying you are an idiot, or a troll, or something. How old are you?
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  44. #43  
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by Mayflow View Post
    I don't know if there is a constant in this or not.
    It was assumed to be constant until Saul Perlmutter, Brian Schmidt and Adam Riess made their Nobel-prize winning discovery.
    Dark Energy Wins Nobel Prize in Physics | Popular Science
    Well, it wasn't assumed to constant, it was assumed that the expansion was decelerating due to the mutual gravitational attraction of the Universe. What they were originally trying to determine was whether or not this deceleration was enough to eventual halt the expansion completely and lead to a collapse.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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  45. #44  
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    Quote Originally Posted by Janus View Post
    Quote Originally Posted by Strange View Post
    Quote Originally Posted by Mayflow View Post
    I don't know if there is a constant in this or not.
    It was assumed to be constant until Saul Perlmutter, Brian Schmidt and Adam Riess made their Nobel-prize winning discovery.
    Dark Energy Wins Nobel Prize in Physics | Popular Science
    Well, it wasn't assumed to constant, it was assumed that the expansion was decelerating due to the mutual gravitational attraction of the Universe. What they were originally trying to determine was whether or not this deceleration was enough to eventual halt the expansion completely and lead to a collapse.
    Yes. I need to study this more because some of the math concerning what Brian and some others came up with is still a bit out from my radar, and the thing also is that we really do not know if the Universe will eventually collapse. Now, the best stuff seems to say it just keeps expanding, which is why the idea of dark energy developed (and won a Nobel prize) - Janus, you should think about joining the course. It is free and no obligations.
     

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    Now, the best stuff seems to say it just keeps expanding, which is why the idea of dark energy developed
    Dark energy was conceived to explain the acceleration of the rate of expansion, not expansion itself. That's explained by Einstein's GR.
    Its the way nature is!
    If you dont like it, go somewhere else....
    To another universe, where the rules are simpler
    Philosophically more pleasing, more psychologically easy
    Prof Richard Feynman (1979) .....

    Das ist nicht nur nicht richtig, es ist nicht einmal falsch!"
     

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    When Albert Einstein developed his theory of general relativity, he realized that they implied an unstable equilibrium position. Any slight unevenness would cause spacetime to expand or contract. He had the philosophical belief (as did most physicists of the time) in a static universe, so he added a constant term which was allowed (but not required) onto the end of his equation when he published the theory in 1916.In 1929, however, the astronomer Edwin Hubble discovered evidence that distant galaxies were receding from our own galaxy. Though Einstein's model, with the cosmological constant, other models by Alexander Friedmann and Willem de Sitter (which didn't include the cosmological constant) had predicted such expansion quite clearly. Einstein quickly accepted the new evidence and told physicist George Gamow that the cosmological constant idea was the "biggest blunder" of his life.
    Cosmological Constant Revisited

    In 1998, two different teams of researchers discovered evidence that the universe's expansion was actually speeding up. This meant that the cosmological constant wasn't just zero, as expected, but had to have a very slight positive value. The theory that has grown up around this positive cosmological constant is the theory of dark energy.
     

  48. #47  
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    When you cut and paste you should give credit to the site you copy from. You also keep posting what amounts to common knowledge here.
    Its the way nature is!
    If you dont like it, go somewhere else....
    To another universe, where the rules are simpler
    Philosophically more pleasing, more psychologically easy
    Prof Richard Feynman (1979) .....

    Das ist nicht nur nicht richtig, es ist nicht einmal falsch!"
     

  49. #48  
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    Quote Originally Posted by Mayflow View Post
    When Albert Einstein developed his theory of general relativity, he realized that they implied an unstable equilibrium position...
    First, it is very bad form to crib from some other source and fail to cite it. In academic circles, this sort of behavior is viewed as extremely dishonest, and often brings appropriately dire consequences. In this case, your paragraph above seems to come from a collection found in various places on the web. See, e.g., http://www.skeptive.com/sources/18570/source_urls/93463.

    Second, this quotation is another of a long string of posts by you in which you simply state something without context. Treating the forum as essentially a form of personal blog is inappropriate. There are better ways for you to assemble links to the works of others.

    ETA: Ninja'd by AlexG!
     

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    Your indignation is misplaced. Embarrassment or shame would be more appropriate.

    As to "happy," that's irrelevant. It's a matter of right and wrong. It's not a trivial matter at all. Presenting someone else's words and thoughts as your own is a major academic foul.

    And all that aside, there's still the matter of the purpose of this thread. What is it? What are your questions about astrophysics?
    Last edited by tk421; April 12th, 2014 at 05:38 PM.
     

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    Good grief (again)

    Which line in the above spectrum has most energy at short wavelengths?


    The blue long-dashed line
    The black short-dashed line
    The red solid line
    The red solid line - correct
    None of the other answers is correct
     

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    You appear to be simply copying questions from your online course. Is there a point to this?
    Its the way nature is!
    If you dont like it, go somewhere else....
    To another universe, where the rules are simpler
    Philosophically more pleasing, more psychologically easy
    Prof Richard Feynman (1979) .....

    Das ist nicht nur nicht richtig, es ist nicht einmal falsch!"
     

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    Considering who the teachers are and how much I can learn, yes I think so. If you do not want to learn from it, I really do not care, but some may, and I do.
     

  55. #54  
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    By all means, take the course and learn. There's just no need to copy it here.
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    Its the way nature is!
    If you dont like it, go somewhere else....
    To another universe, where the rules are simpler
    Philosophically more pleasing, more psychologically easy
    Prof Richard Feynman (1979) .....

    Das ist nicht nur nicht richtig, es ist nicht einmal falsch!"
     

  56. #55  
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    Quote Originally Posted by Mayflow View Post
    Considering who the teachers are and how much I can learn, yes I think so. If you do not want to learn from it, I really do not care, but some may, and I do.
    Again, this forum is not to be treated as anyone's personal blog. As entertaining as random science quizzes might be for you, they don't belong in the main section. And as AlexG has pointed out, the rest of us didn't sign up for your class, so copying and pasting that course material here is not appropriate. (And your continued use of that material without attribution remains troublesome.)

    You seem not to have learned much from your first suspension, nor from the advice given to you about your attitude. Your immaturity is going to get you banned at this rate.

    Your choice.
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    Quote Originally Posted by AlexG View Post
    By all means, take the course and learn. There's just no need to copy it here.
    Maybe my mistake. I thought some may learn and participate, but if you don't want to, well just go to other topics, ok?
     

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    Quote Originally Posted by Mayflow View Post
    Quote Originally Posted by AlexG View Post
    By all means, take the course and learn. There's just no need to copy it here.
    Maybe my mistake. I thought some may learn and participate, but if you don't want to, well just go to other topics, ok?
    It is your mistake to assume that lectures are appropriate here. This is a forum for discussion. Get it?
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  59. #58  
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    Really and seriously, for those who do not want to participate in the topic, just don't. How simple is that?
     

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    Quote Originally Posted by Mayflow View Post
    Really and seriously, for those who do not want to participate in the topic, just don't. How simple is that?
    Really and seriously, just don't abuse the forum. How simple is that?

    You still won't get it, of course. So let me try something else:

    I'm going to spam your home with incessant phone calls and junk mail. Really and seriously, for those who don't like spam, just don't read the mail, and don't answer the calls. How simple is that?
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  61. #60  
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    Quote Originally Posted by Mayflow View Post

    The red solid line - correct
    This one.
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    "Ok, brain let's get things straight. You don't like me, and I don't like you, so let's do this so I can go back to killing you with beer." - Homer
     

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    Apparently as simple as asking you to stop spamming my topic! Do you mind either replying to my topic or just going somewhere else?
     

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    This isn't 'your' topic. When you post on this board, it's all public.
    Its the way nature is!
    If you dont like it, go somewhere else....
    To another universe, where the rules are simpler
    Philosophically more pleasing, more psychologically easy
    Prof Richard Feynman (1979) .....

    Das ist nicht nur nicht richtig, es ist nicht einmal falsch!"
     

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    Quote Originally Posted by SpeedFreek View Post
    Quote Originally Posted by Mayflow View Post

    The red solid line - correct
    This one.
    Yeah, the red line had a higher flux at a lower wavelength. You are like the only guy here to actually address the questions, although I actually said which answer was correct this time. I will tell you, that some of the test questions so far are beyond me, but the idea is to learn.
     

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    Quote Originally Posted by Mayflow View Post
    Apparently as simple as asking you to stop spamming my topic! Do you mind either replying to my topic or just going somewhere else?
    Thanks for the options, but I prefer not to have you spam this forum. I've given you good advice, you've refused to take it (as is your right). But this is a community here, not your private blog or notebook of "science facts that I've learned." And communities have social norms. To ignore that is to create problems. Your arrogant belief that only your desires matter has already gotten you into trouble here. I guess you are hell-bent on getting the boot.
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    I take it you want to keep spamming my topic? Why not make a topic of your own? I promise to not even visit it.
     

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    Quote Originally Posted by Mayflow View Post
    I take it you want to keep spamming my topic? Why not make a topic of your own? I promise to not even visit it.
    Please re-read my reply to post 64.

    You really should take my advice. From the other discussion you launched, you refuse to consider that you are the primary source of the problems you have encountered here. That's going to lead to more unhappiness for you.
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    Quote Originally Posted by Mayflow View Post
    Yeah, the red line had a higher flux at a lower wavelength.
    Okay, here's a question for you that's "on topic" 1: WHY does it have most energy?

    1 I'm guessing here, because I have no idea what the "topic" is, unless it's a Blog of Ignorance.
    "[Dywyddyr] makes a grumpy bastard like me seem like a happy go lucky scamp" - PhDemon
     

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    I fail to see what that has to do with astrophysics.
     

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    Quote Originally Posted by Mayflow View Post
    I fail to see what that has to do with astrophysics.
    Exactly.

    And by implication, your "quiz" similarly is irrelevant.

    See the problem now? (I'm guessing not.)
     

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    Quote Originally Posted by Mayflow View Post
    I fail to see what that has to do with astrophysics.
    Another way to say 'I don't know'.
    Its the way nature is!
    If you dont like it, go somewhere else....
    To another universe, where the rules are simpler
    Philosophically more pleasing, more psychologically easy
    Prof Richard Feynman (1979) .....

    Das ist nicht nur nicht richtig, es ist nicht einmal falsch!"
     

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    Considering who the teachers are and how much I can learn, yes I think so. If you do not want to learn from it, I really do not care, but some may, and I do.
    Apparently as simple than asking you to stop spamming my topic! Do you mind either replying to my topic or just going somewhere else?
    I take it you want to keep spamming my topic? Why not make a topic of your own? I promise to not even visit it.
    Really Mayflow.

    You seem not to understand what these forums are for. It is entirely appropriate for people doing a course, online or otherwise, to bring questions to the forum or to report that they've found the Best Explanation Ever for a topic they've previously found confusing or incomprehensible but you're not doing that.

    Protip: When you do that you always, always, always give the citation, preferably a link - without being asked.

    What we do not do here, and you must stop doing it, is to behave like a little kid lining up all their teddies for them to play schoolteacher.

    It's not your job to teach or to test anyone here. Plenty of people here guide or coach or inform or educate others who have queries or confusions they want help with. Until someone asks for help or advice that you are competent to give, don't do it. If you've read something relevant to someone's questions, give them a handy link along with your own understanding or experience of using it.

    And you don't own any thread here. It's not your space, it's our shared space. If you want to control a discussion and who participates in it and how they participate, start your own blog. This is a casual common room. It's not hired out as a private lecture theatre.

    Thread closed.
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