So analyzing the spectrum of a star and comparing that to the spectrum of the reflected light of a planet wouldn't disprove the oort cloud star theory?If our nearest star is not a star, and what we are seeing is reflected sunlight, then could there be some way to send out a 'signal' of some sort that would be reflected back to us?
And seeing as I am flying by the seat of my pants with all this stuff, IWe present the geometrical optics for refraction of a distant background radio source by an interstellar plasma lens, with specific application to a lens with a Gaussian profile of free-electron column density.
http://iopscience.iop.org/0004-637X/496/1/253
Gary, are you saying only hydrogen is detectibale?So, if you look at Sirius and see H emissions, you
assume it is a star, when it might just be what we see when looking at a glowing charge
field around a planet.
I think this is hard science and I didn't glaze over reading it.http://imagine.gsfc.nasa.gov/docs/scien ... _what.html
The chemical composition of stars
During the first half of the 19th century, scientists such as John Herschel, Fox Talbot, and William Swan studied the spectra of different chemical elements in flames. Gradually, the idea that each element produces a set of characteristic emission lines was established. Each element has several prominent, and many lesser, emission lines in a characteristic pattern. Sodium, for example, has two prominent yellow lines (the so-called D lines) at 589.0 and 589.6 nm -- any sample that contains sodium (such as table salt) can be easily recognized using this pair of lines.
The studies of the solar spectrum (Joseph Fraunhofer is the most famous and probably also the most important early contributor to this field), however, revealed absorption lines (dark lines against the brighter continuum). The precise origin of these 'Fraunhofer lines', as we call them today, remained in doubt for many years, until Gustav Kirchhoff, in 1859, announced that the same substance can either produce emission lines (when a hot gas is emitting its own light) or absorption lines (when a light from a brighter, and usually hotter, source is shone through it).Now scientists had the means to determine the chemical composition of stars through spectroscopy!
One of the most dramatic triumphs of astrophysical spectroscopy during the 19th century was the discovery of helium. An emission line at 587.6 nm was first observed in the solar corona during the eclipse of August 18, 1868, although the precise wavelength was difficult to establish at the time (due to the short observation using temporary set-ups of instruments transported to Asia). Two months later, Norman Lockyer used a clever technique and managed to observe solar prominences without waiting for an eclipse. He noted the precise wavelength (587.6 nm) of this line, and saw that no known terrestrial elements had a line at this wavelength. He concluded that this must be a newly discovered element and called it 'helium'. Helium was discovered on Earth eventually (1895) and showed the same 587.6 nm line. Today, we know that helium is the second most abundant element in the Universe.We also know today that the most abundant element is hydrogen. However, this fact was not obvious at first. Many years of both observational and theoretical works culminated in 1925, when Cecilia Payne published her PhD thesis entitled 'Stellar Atmospheres'. (Footnote: this was the first ever PhD awarded at Harvard; it was also praised as "undoubtedly the most brilliant PhD thesis ever written in astronomy" nearly 40 years later. She later turned to studies of variable stars, and coined the term 'cataclysmic variables'.) In this early work, she utilized many excellent spectra taken by Harvard observers, and measured the intensities of 134 different lines from 18 different elements. She applied the up-to-date theory of spectral line formation and found that the chemical compositions of stars were probably all similar, with the temperature being the important factor in creating their diverse appearances. She was then able to estimate the abundances of 17 of the elements relative to the 18th, silicon. Hydrogen appeared to be more than a million times more abundant than silicon, a conclusion so unexpected that it took many years to become widely accepted.
).
No, not at all Frank. That device they had on the Moon was set up just to seeGary, are you saying only hydrogen is detectibale?
If they are stars.Now scientists had the means to determine the chemical composition of stars through spectroscopy!
I'm not sure how accurate spectroscopy can be either, at great distances.I was wondering about just how accurate or dependable our observation methods were,http://iopscience.iop.org/0004-637X/496/1/253 ? I read some and glazed over pretty fast. You are going to have to simplify things, to explain it to me.
Not with a 100 watt bulb. Replace that with a tiny electric arc, andIf I place a hundred watt light bulb at a scaled distance of the oort cloud and through a bucket of sand in the air and you being at the scaled distance of the earth to the sun. Are you going to see the individual sand reflections as we see stars?
An elephant should be an easy target! I suspect you are way more knowledgeable thanI kind of feel weird, cause such heavy weights have posted on this thread, and not discussed the elephant in the room.
Maybe Our Sun is the primary, it is supposedly, and I do agree our distance estimates for the nearer objects are improving steadily, 4.37 light years away. It is not to do with the albedo if the emissions are from aIf you think that those stars are just planets reflecting some other star's light toward Earth, which star do you choose as their primary? How many light years away are those three "planets" from their primary? How bright is the primary's light by the time it gets to α Cen A, and how high is the albedo to reflect that distant light over to Earth across 4.37 more light years? I don't buy it.
Your inverse square law does not apply if the waves are planewaves,Do the 1/r² math for light falloff over distance
I have some doubts. Some of those objects are as large as the moon profile. More likely it's dust, rocks etc. as the sun, which must be to Messengers side, will act like an immense flash bulb.nick c wrote:Also, there appear to be plenty of stars in the view.
I suspect that image is from the UV spectrometer, and not the Dual Imaging System, but have not foundI have some doubts. Some of those objects are as large as the moon profile. More likely it's dust, rocks etc. as the sun, which must be to Messengers side, will act like an immense flash bulb.nick c wrote:
Also, there appear to be plenty of stars in the view.
My first thought was that the bright dots were stars... Notice how the Earth and to a lesser extent, the Moon, are greatly overexposed. Remember (and I am assuming that this is more or less a wide angle view, i.e. not telephoto) that Earth and Moon would not be visible as disks from Mercury. That, they look like disks in the photo, is because of they are so bright that they are overexposed. That means the camera could pick up fainter objects like stars.
NickIndeed, Nicholas, those are stars.
Mike CarlowiczEditor - NASA Earth Observatory - http://earthobservatory.nasa.gov774-413-5168 (home office) and 508-566-2620 (cell)michael.j.carlowicz@nasa.gov
Yet that doesn't explian why some of the stars are large multi-pixel objects. Surely the stars wouldn't be overexposed.nick c wrote:From the image linked to in the post by D_Archer:My first thought was that the bright dots were stars... Notice how the Earth and to a lesser extent, the Moon, are greatly overexposed. Remember (and I am assuming that this is more or less a wide angle view, i.e. not telephoto) that Earth and Moon would not be visible as disks from Mercury. That, they look like disks in the photo, is because of they are so bright that they are overexposed. That means the camera could pick up fainter objects like stars.
NASA seems to agree with that assessment, and I have no reason to doubt their veracity. I emailed them and asked if the image showed the background stars, here is the response:NickIndeed, Nicholas, those are stars.
Mike CarlowiczEditor - NASA Earth Observatory - http://earthobservatory.nasa.gov774-413-5168 (home office) and 508-566-2620 (cell)michael.j.carlowicz@nasa.gov
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