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Old science thoughts in new science packages
Posted: 20 February 2012 12:02 PM   [ Ignore ]   [ # 16 ]
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Doug and Gdb,

Yes! Wavelength is NOT speed. Doh! Brain fart, but now I feel better. Thanks both of you. I was conflating energy, wavelength and speed.  grin

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Posted: 20 February 2012 03:40 PM   [ Ignore ]   [ # 17 ]
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I am even more confused by the fact that stars have a specific color signature from their composition. How can we tell we know which is which?
Theoretically we could have a “red” star moving toward us and be slightly blue shifted, but still appear red. And vice versa with a “blue” star moving away from us still appearing blue.
Can we accurately measure the composition of stars and know what their inherent color signature is?

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Posted: 20 February 2012 03:50 PM   [ Ignore ]   [ # 18 ]
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Write4U - 20 February 2012 03:40 PM

I am even more confused by the fact that stars have a specific color signature from their composition. How can we tell we know which is which?
Theoretically we could have a “red” star moving toward us and be slightly blue shifted, but still appear red. And vice versa with a “blue” star moving away from us still appearing blue.
Can we accurately measure the composition of stars and know what their inherent color signature is?

You tell the composition of the star by looking at the emission spectrum (or absorption spectrum for telling the composition of its atmosphere). These present as a group of dim and bright, differently spaced lines, arrayed in patterns each of which is an indication of a particular chemical element.

The spectral lines retain the same patterns over red or blue shifting, they simply move farther along the spectrum. If you see a pattern of lines for hydrogen, but the lines appear shifted to the red, that tells you that the hydrogen source is moving away from us at a high rate of speed.

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Posted: 20 February 2012 04:14 PM   [ Ignore ]   [ # 19 ]
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ah. ok. We measure by breakdown of the signature spectrum of the predominant elements, not by its general appearance.

[ Edited: 20 February 2012 04:18 PM by Write4U ]
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Posted: 20 February 2012 04:17 PM   [ Ignore ]   [ # 20 ]
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Write4U - 20 February 2012 04:14 PM

ah. ok. We measure by breakdown of the spectrum of the predominant elements, not by its general appearance.

I ... think so. I mean, we do measure the spectrum by its general appearance; I suppose it depends what you mean by the phrase.

It’s just that the lines can be shifted across the spectrum by the doppler effect.

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Posted: 20 February 2012 04:33 PM   [ Ignore ]   [ # 21 ]
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dougsmith - 20 February 2012 04:17 PM
Write4U - 20 February 2012 04:14 PM

ah. ok. We measure by breakdown of the spectrum of the predominant elements, not by its general appearance.

I ... think so. I mean, we do measure the spectrum by its general appearance; I suppose it depends what you mean by the phrase.

It’s just that the lines can be shifted across the spectrum by the doppler effect.

Perhaps I should have added the word signature spectrum “pattern” of elements, which is recognizable as unique to each element? Then even as the pattern condenses or stretches it would still retain it signature.  Much like writing the same word in a condensed way or stretched way. It remains the same word (order of letters).

[ Edited: 20 February 2012 04:38 PM by Write4U ]
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Posted: 20 February 2012 05:29 PM   [ Ignore ]   [ # 22 ]
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Write4U - 20 February 2012 04:33 PM

Perhaps I should have added the word signature spectrum “pattern” of elements, which is recognizable as unique to each element? Then even as the pattern condenses or stretches it would still retain it signature.  Much like writing the same word in a condensed way or stretched way. It remains the same word (order of letters).

Works for me.

Fun refresher.

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Posted: 20 February 2012 06:03 PM   [ Ignore ]   [ # 23 ]
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It’s funny how the human memory works.  I learned all that stuff about sixty years ago, but never had any occasion to think about it. Now, I read this thread, and the information all comes flooding back.  Strange how it can just sit there unused for more than half a century then, on some stimulus, there it is.

Occam

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Posted: 20 February 2012 06:47 PM   [ Ignore ]   [ # 24 ]
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Occam. - 20 February 2012 06:03 PM

It’s funny how the human memory works.  I learned all that stuff about sixty years ago, but never had any occasion to think about it. Now, I read this thread, and the information all comes flooding back.  Strange how it can just sit there unused for more than half a century then, on some stimulus, there it is.

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Posted: 20 February 2012 06:52 PM   [ Ignore ]   [ # 25 ]
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Write4U - 20 February 2012 04:33 PM

Perhaps I should have added the word signature spectrum “pattern” of elements, which is recognizable as unique to each element? Then even as the pattern condenses or stretches it would still retain it signature.  Much like writing the same word in a condensed way or stretched way. It remains the same word (order of letters).

Right. I’ve heard that once you learn to recognize the spectral patterns of each element, you can see them very clearly even when they’ve been shifted. (And of course each stellar spectrum will be an amalgam of all the lines from the various elements in the star).

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Posted: 20 February 2012 07:37 PM   [ Ignore ]   [ # 26 ]
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I just occurred to me that one critical thing that sets man apart from all other animals, is the ability to translate different languages (in any form).

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Art is the creation of that which evokes an emotional response, leading to thoughts of the noblest kind.
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Posted: 20 February 2012 11:43 PM   [ Ignore ]   [ # 27 ]
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Write4U - 20 February 2012 03:40 PM

Theoretically we could have a “red” star moving toward us and be slightly blue shifted, but still appear red. And vice versa with a “blue” star moving away from us still appearing blue.

Write, look at the spectrum of Saturn here. You can see that the lines are shifted. The light is of course exactly the same, it is the reflected light of the sun. It is just by the velocity of the particles that form the rings, and the turning of Saturn itself that the lines are shifted.
In a workgroup during my study I actually measured the velocities with such a picture (therefore I got the idea to search for such a picture in the internet). It is just applying a few simple Doppler effect formulas, pretty basic.

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Posted: 21 February 2012 12:02 AM   [ Ignore ]   [ # 28 ]
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Traveler,

I looked it up yesterday in a book of mine in a chapter called ‘a zoo of redshifts’...

The following example was given, a thought experiment. Two galaxies exist in a static universe, i.e. their universe is not expanding. Then galaxy A sends a light beam to galaxy B. Shortly after, the universe starts expanding, but before the light beam reaches galaxy B, the expansion stops again. Now the light beam is not red shifted because of the doppler effect, the galaxies are standing still again. But the universe itself has expanded, which means the light beam has expanded too, i.e. got a longer wavelength, which means it has red shifted. Does that help?

Edit: but see here...

[ Edited: 21 February 2012 12:20 AM by GdB ]
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Posted: 21 February 2012 01:58 AM   [ Ignore ]   [ # 29 ]
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GdB - 20 February 2012 11:43 PM
Write4U - 20 February 2012 03:40 PM

Theoretically we could have a “red” star moving toward us and be slightly blue shifted, but still appear red. And vice versa with a “blue” star moving away from us still appearing blue.

Write, look at the spectrum of Saturn here. You can see that the lines are shifted. The light is of course exactly the same, it is the reflected light of the sun. It is just by the velocity of the particles that form the rings, and the turning of Saturn itself that the lines are shifted.
In a workgroup during my study I actually measured the velocities with such a picture (therefore I got the idea to search for such a picture in the internet). It is just applying a few simple Doppler effect formulas, pretty basic.

Yes. thanks GdB, I saw that pick in post #12 The shift is clearly visible by the tilting lines in the middle spectrum of Saturn itself. Same line pattern but slightly slightly shifted.
I was also wondering about some of the signature lines in the outer rings. The top pictures of the rings shows a few fainter lines, which are not visible in the bottom pic of the rings. Obviously they are still pics of the rings at opposite sides of Saturn. What would account for that?
Visual interference or a gap in a specific part of the ring?

[ Edited: 21 February 2012 02:03 AM by Write4U ]
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