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Ο "Andrew Urquhart" έγραψε στο μήνυμα news:_0m1c.103$m56.92@newsfe1-win... [snip] You're going to need a good few photons to be able to remove the uncertainty as to peaks and troughs in the wavelength profile. In this recent story: http://www.astronomynow.com/news/040...t_galaxy.shtml I imagine they had enough photons to calculate an approximate blackbody curve to determine the redshift, but I very much doubt they could tell you what the composition of the galaxy was! Agreed, but I took the OP question to refer to individual objects. For (strange) galaxies, I wouldn't even bother, since as many people have pointed out, the resultant spectra are simply integrated over thousands of individual sources. If one takes the spectrum of a quazar or some otherwise strange object like a Seyfert galaxy, which often exhibit various emission wavelengths, the spectral analysis is difficult to begin with, when it relates to "who emits what", so I would imagine that such attempts carry much less info for complex objects than for individual objects, unless there is some additional evidence on the emitters and their individual spectra. From a practical standpoint, I am even not sure what it would mean to say "the spectrum of a strange/distant composite object is such and such". That's like me putting together in a box 100 discharge tubes with different elements, mix their light together and pass the resulting light through a Lambertian diffuser and then after analyzing the light, saying "well, the "object" appears to consist of Hg, Na, Th, In, Sc, ...". Doesn't make much sense to me, unless I have _some_ idea about the individual components that sit inside that box. For example, for a regular galaxy, like M31, what kind of info can one get if one maps the spectrum of the galaxy as a whole? I presume the dominant radiation would come from the statistically dominant star types. That tells one something about the larger population of stars of M31, but doesn't otherwise say much about the less prominent members of it, which may well exist and their radiation may be hidden from all the integrated "noise" from the dominant star population. I imagine the situation would be much more difficult with quazars, where the exact mechanisms of their spectra emissions are not even known well enough to guarantee some sort of selective filtering and analysis. What do the emission lines from quazars actually denote? That we have individual members who have emission lines or that there is some other mechanism which is responsible for the emission as being the predominant radiation? -- Andrew Urquhart Reply: www.andrewu.co.uk/about/contact/ -- Ioannis Galidakis http://users.forthnet.gr/ath/jgal/ ------------------------------------------ Eventually, _everything_ is understandable |
#12
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"beavith" wrote
[Uh, like... words and stuff] Settle down, Beavis! What's your problem? |
#13
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"Martin Brown" wrote in message ... In message , Ioannis writes ? "Abdul Ahad" ?????? ??? ?????? . com... What is the faintest "source" that can be spectroscopically analysed via a telescope for fraunhofer lines and elemental composition? A devious answer to this is that we can analyse clouds of hydrogen gas that happen to be in the line of sight between us and a distant quasar no matter how faint the cloud itself may be. The light from the quasar allows us to see the composition and redshift of the intervening gas cloud. Hi Martin, Do you have a reference for this? I want to be able to give a proper reference to people who claim that red-shift is due to 'tired light' Cheers Owen |
#14
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In message , Tony
Flanders writes As for other people's comments, barring the ability to measure the energy of individual photons -- which is *not* currently possible in the visible spectrum -- of course you need more light to do spectroscopy than to do simple photography. How much more depends on how finely you want to resolve those spectral lines. Measuring the energy of individual visible light photons was once a popular technique in the late 70's combining a large scope, spectrometer and Boksenberg's Image Photon Counting System to do exactly that task. It opened up the possibility of obtaining spectra from very much fainter objects than was possible with conventional film emulsions. Wavelength dispersion determines the energy, and the imaging system is sensitive to single photons with good QE at suitably low intensities. There are noise problems with it, but for a while it was the method of choice. Now largely supplanted by CCDs, but I think it is still used for certain jobs. Regards, -- Martin Brown |
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In message , OG
writes "Martin Brown" wrote in message ... In message , Ioannis writes ? "Abdul Ahad" ?????? ??? ?????? . com... What is the faintest "source" that can be spectroscopically analysed via a telescope for fraunhofer lines and elemental composition? A devious answer to this is that we can analyse clouds of hydrogen gas that happen to be in the line of sight between us and a distant quasar no matter how faint the cloud itself may be. The light from the quasar allows us to see the composition and redshift of the intervening gas cloud. Hi Martin, Do you have a reference for this? I want to be able to give a proper reference to people who claim that red-shift is due to 'tired light' Google "Lyman forest" ought to bring something useful up. Combine it with "tired light" and you may get exactly what you seek. Regards, -- Martin Brown |
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On Thu, 4 Mar 2004 21:52:44 -0000, "Fleetie"
wrote: "beavith" wrote [Uh, like... words and stuff] Settle down, Beavis! What's your problem? he hehe HE he he kick your ass he eh hehe. |
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#20
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Martin Brown wrote:
[ text omitted ] Hi Martin, Do you have a reference for this? I want to be able to give a proper reference to people who claim that red-shift is due to 'tired light' Google "Lyman forest" ought to bring something useful up. Combine it with "tired light" and you may get exactly what you seek. Regards, Martin: 'Tired light' is a term that suits then advocates of the BB; it is a derogatory term that is intended to place an emotional wet blanket upon the issue in order to discredit any possible explanation for a physical cause of the diminution of the energy levels of photons as they traverse the openness of space. If you grant the recognition of physical reality to the existents in space, rather than trying to create a metaphysical reality out of an epistemological mathematical graphical concept of the instant locations of gravitational acceleration forces, i.e., curved space-time, you may find that there are causes for the "Apparent Red Shift" of light that do not depend upon the Hubble - Doppler creationist-expansionist BB theory. The proper scientific question to ask is, "What happens to light photons as they traverse to openness of outer space that causes the diminution of their energy levels?" The issue is whether mathematical EM waves, that have no physical existence, except insofar as the waves are the properties of actual physical existents, i.e., photons, are valid as a metaphysical concept. Or whether physical existents, i.e., light photons, actually have physical properties that in interactions with other physical existents, for example, gravitons or photons, can have different energy levels. In terms of the validity of methods of scientific proof, the method of 'application' is an inferior method proof for the identification of causal relationships. For example, if, due to the "Apparent Red Shift" and the hypothesized "Doppler Effect", some Euclidean straight lines are made to represent velocity or distance vectors, and those lines are extended in reverse to some claimed point of intersection, or central point or origin, the universe is claimed to not have existed prior to that geometric extension - you know you have a problem. The fact of existence is that existence is what it is, and that it continues to exist as what it is. There is no reason to claim that the universe ever did not exist or ever will exist, and that there is every reason to know that the plurality of the universe exists continually. Period. If you claim the Biblical creationist-expansionist -Euclidean -Hubble -Doppler theory that leads to the suggestion of the origin of the universe you must at the same time deny the principle of the continuity of the plurality of universe and of all its changing existents. BB advocates can never, for that reason find what happens to photons in their travels that causes the "Apparent Red Shift". BTW, the Post modernist mathematical argument that Euclid's "Parallel Postulate" is invalid because parallel lines are impossible or that projected lines can never meet throws cold water on the BB proposition. To arrive at the BB hypothesis the BB advocates must admit to the validity of Euclid's Parallel Postulate and quite a few other proved propositions, definitions, and axioms from, at least, Book I of Euclid's "Elements". Existence is existing, and logic, inductive and deductive, is competent to know the facts of the constituent existents and properties of the plural universe, their relationships, potentials for change, and their resulting identities. Ralph Hertle |
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