It seems to me that the alternative models for the sun, introduced now in several threads, all suffer from a considerable lack of appreciation for the strong foundations of the standard model for the sun. So, I start this thread with two ideas in mind.

1) I will start by giving a brief historical account of how the current standard model came to be, and I will finish it up with a reference to my own webpage on the sun.

2) The continuing discussion should avoid any direct discussion of alternative models, and concentrate on the sole topic of the viability of the standard model. What's wrong with it? Does it fail some empirical test? Is it incompatible with observation? Does it violate the laws of physics? Why is the standard model supposed to be so bad? Why do we need an alternative anyway?

Historical introduction to the standard model

The first edition of Encyclopedia Britannica (1771) describes the sun as an "immense globe of fire". The description in Thomas Squire's A Popular Grammar of the Elements of Astronomy (London, 1820, the oldest astronomy book in my library) is no different. Indeed, prior to the mid 1800's, astronomy books pretty much avoid the stars, and spend lots of pages talking about the solar system. They simply didn't know what stars were.

A major breakthrough in understanding the sun comes in the late 1800's, in two books by J. Norman Lockyer: Studies in Spectrum Analysis (1878) and Elements of Astronomy (1886). The science of spectroscopy had been discovered decades before (see history of spectroscopy for details), but these books deliver the first discussions of a complete study of spectroscopy applied to the sun. In Neither book does Lockyer make any definitive statement as to the elements that make up the sun, but he does list the number of spectral lines observed, and they are all metals, iron having the most spectral lines visible. It was from this time that the then standard model of the sun held that it was made mostly of heavy elements, as were the planets. After all, at the time, there was no reason to believe that the constituent elements of the sun were remarkably different from the planets, even though its temperature was known to be much higher.

It is also worth notice that in his 1886 book, Lockyer speculated on whether or not the sun could be inhabited. He did realize that no living creature could withstand the high temperature of the photosphere. But it was unknown at that time, whether sunspots provided a view of a solid surface below the hot photosphere. Lockyer speculates that something could live on such a surface, if it could avoid the heat.

Simon Newcomb's 1906 book, The Stars - A Study of the Universe, is the oldest astronomy book I have that concentrates on stars, rather then planets. But even here, Newcomb says nothing specific about the chemical constituents of the stars, other than to briefly relate the spectroscopic studies of Lockyear, and others. At the turn of the 19th/20th centuries, it was still not known what the stars were really made of, but it was known that heavy metals were most evident in the spectra.

The first "real" book on stellar physics is Eddington's Internal Constitution of the Stars (1926). It was followed by Charles G Abbot's less technical, but more specific book, The Sun (1929). By this time Eddington had demonstrated that the sun (and stars in general) could not be made mostly of heavy elements (i.e., metals), because the opacity of these elements lead to internal pressures that do not permit them to have the observed brightness & radius (by proxy with the sun, the only star close enough to get a radius for). Not everyone went along with Eddington, and Abbot relates that Jeans argued that the core of the sun must be made of heavier elements, specifically uranium and heavier. Eddington & Jeans were on opposing sides in the argument over the chemical constituents of the sun.

In the ensuing years, Eddingtons arguments won out. Perhaps the single most significant piece of research was that done by the American astronomer Henry Norris Russell: On the Composition of the Sun's Atmosphere, Astrophysical Journal 70: 11-82, July, 1929. Russell made it quite clear that the atmosphere of the sun, the part we could see, was mostly hydrogen, despite all of the metal lines seen by early spectroscopists. Other important papers followed, which served only to strengthen the move away froma "mostly metals" sun (i.e., Notes on the constitution of the stars, H.N. Russell, Monthly Notices of the Royal Astronomical Society 91: 951-966, June 1931; The opacity of stellar matter and the hydrogen content of the stars, Bengt Stromgren, Zeitschrift für Astrophysik 4: 118-152, 1932; On the Helium and Hydrogen Content of the Interior of the Stars, Bengt Stromgren, Astrophysical Journal 87: 520-534, June 1938, to cite just a few). It had become increasingly clear that the sun was made mostly of hydrogen & helium.

While the chemical constituency of the sun was under discussion, so too was its source of energy, which was perhaps even more mysterious. Nevertheless, by the time Eddington had written Internal Constitution of the Stars, it was evident that some kind of nuclear process was responsible, though nuclear fusion was as yet unknown. When Chandrasekhar wrote his book, An Introduction to the Study of Stellar Structure, in 1938 (published in 1939), it was well understood that (a) the sun ws made mostly of hydrogen, and (b) some nuclear process was responsible for energy generation in the core of the sun.

The problem of energy generation by fusion was finally solved by Hans Bethe, who eventually was awarded a Nobel Prize, primarily for this discovery (The Formation of Deuterons by Proton Combination, H.A. Bethe & C.L. Critchfield, Physical Review 54(4): 248–254, 15 August 1938; Energy Production in Stars, H.A. Bethe, Physical Review 55(1): 103, 1 January 1939; Energy Production in Stars, H.A. Bethe, Physical Review 55(5): 434–456, 1 March 1939).

So, while Eddington, Russell, Stromgren & others had settled the chemical constituency of the sun, Bethe & Critchfield had also settled its source of energy. This was the status of solar study, when WWII started. This basic model of the sun, a mostly hydrogen gas spheroid has remaind intact since then, though in the ensuing 65 years or so, a great deal of additional advancement has been made in understanding the solar interior, and especially the chromosphere, corona & solar wind, which were still not well understood at that time.

Here I will break off the narrative, and refer the reader to my webpage: Solar Fusion & Neutrinos. On that page I give a fairly up to date description of the fusion processes, and a discussion of the solar neutrino problem. I have also included copious references to webpages, and books for further reading (some of which are suitable for the non mathematically inclined reader). Those books & webpages will bring you up to date on the details of current thinking in solar astrophysics. But I wanted to establish a historical context here, that is not on the webpage.

I think it is noteworthy, especially in light of models suggested both by Mozina & Manuel, that there was a time when the standard solar model was in fact, a mostly iron sun. But that model was abandoned as astronomers & physicists learned more & more about the sun. They discovered that such models simply could not survive scrutiny, and there has been no good reason, yet, to go back to the old models.

So we are left with the eminal question: What's wrong with the standard solar model?