Michael Mozina wrote:
Nereid wrote:If astronomers don't have a bottle of 'nebula material' to test, in their labs, how can they be sure it's composed of O, H, S, etc?
I can see unique spectral lines that can be reproduced in tests of various elements on earth. I have no reason to believe atoms behave differently at a distance or that distant atoms would emit light any differently than they emit here on earth. I therefore have no problem with the concept.
Which is, of course, not an answer to the question asked.
The logic - or assumptions - are, no doubt, common ("I have no reason to believe otherwise, therefore the nebula is composed of O, H, S, etc").
And, in some loose sense, it is also consistent with the nature of science - theories as the engine, viable alternative theories (and tests thereof) are how progress is made.
Although this takes us away from what this thread is about, it is encouraging to see that, at least in this loose sense, consistency with the nature of science*.
It's how the concept gets used as it relates to determining solar composition I object to, mainly because it is based on the assumption that plasmas do not mass separate on the sun. I see no evidence that this particular assumption is valid.
Interesting ... perhaps we could examine this in another thread?
The relevant spectra - emission or absorption - of H, O, or S (in any appropriate state of ionisation) are indeed quite distinct.
And because the emission wavelengths are unique to various elements, we can indeed link specific wavelength to specific elements.
But without a bottle of 'nebula material' in your hand (or you lab), how can you be sure - really sure - that what you see through your telescope was indeed emitted (or absorbed) by H, O, or S?
Why would we have any reason to believe that atoms behave differently at a distance than they behave here on earth as it relates to which wavelengths of light they tend to emit?
Or, going down a level: the spectra of H, O, and S (in any appropriate ionisation state, or any other element, or even compound) can be understood in terms of a 20th century theory in physics.
If you decide - ignore for now how you decided - that the 'nebula material' does indeed include H, O, and S, to what extent is your decision equivalent to a statement (or belief?) about the universality* of that particular 20th century theory of physics?
Hmm. I would not call it a pure statement of 'faith' in the sense that the spectral connection to various elements is fully reproduceable and lab testable any time any one wishes to test the idea.
Here's a good place to introduce something important - let's call it 'extrapolation' - as it is common in astronomy.
There are many spectral lines, seen in astronomical objects, that have not been produced in labs here on Earth.
Further, if we examine the spectra in greater detail - looking at relative line strengths, line profiles, etc - earthly labs fall even more short, in terms of being able to produce what astronomers regularly observe.
And the reason is very simple: earthly labs cannot produce the conditions in which spectra that correspond to what astronomers observe would (should) be seen.
So all you have to do, to get an inconsistency between 'can be produced in labs here on Earth' and astronomical spectra is go down one level in detail (relative line strengths, line profiles, etc).
Of course, this is not a problem, in modern astronomy, because the underlying (quantum) theory very nicely accounts for what astronomer observe ... and so, turning this around, astronomers use the relative line strengths, line profiles, etc to estimate the physical conditions of (in) the nebula, photosphere, etc from which the photons come.
However, it would seem to be a considerable problem for the Michael Mozina (non-standard) variety of astronomy. Is it?
On the other hand there are aspects of astronomy that cannot be tested or falsified.
In this particular example you cited if we have any doubts about the relationship between wavelengths and various atoms, we can certainly test these ideas right there on earth, right now. No actual leaps of faith are required.
Actually, there are ... as I just explained ... let's explore this some more ...
I'm sure you'd agree that we cannot test, in any earthly lab, how a system of three compact objects, of masses ~10^30, ~10^27, and ~10^26 kg, separated by distances of ~10^12 m, behaves, under their mutual gravitational influence. Similarly, we cannot test, in any earthly lab, how such a system of compact objects behaves under their mutual magnetic, electrical, nuclear (weak or strong), ... influence either.
Ergo, a 'leap of faith' is required.
Or maybe not ... would you be so kind as to tell us how this works, in your view of astronomy (as a science)?
*kovil's post, and many of harry's posts, are a good foil in this regard - even this basis seems to be absent.