Gravitation as between the sun's hydrogen atoms causes their electrons to collide. This results in ionization and free protons, which, owing to their mutual gravitational interaction being so much stronger than that of electron
interaction, become the dominant free charge form and give the sun a
positive core charge, thereby causing the sun to have a uniform mass
density. This is set by the balance of the free-proton electrostatic
repulsion and the sun's overall gravitational attraction. The sun has
therefore a mass density of 1.41 gm/cc which is defined by dividing the
mass of the hydrogen atom by the cube of the diameter of the Bohr orbit
of the electron motion. What, however, determines the sun's
temperature? That is the subject discussed below.
By showing students how to derive this equation, which tells us the sun has a temperature of 5,695 K, in agreement with the heat radiation as measured, they will surely see why their basic knowledge of physics is so important. Our very existence depends upon the energy we receive from the sun. Students of today face a future during which oil reserves will diminish dramatically. The sun's heat derives from energy tapped from the quantum underworld that keeps electrons in motion in their parent atoms. It does not come from nuclear fusion! So there is a major lesson to learn and those who teach physics today must heed the evidence here presented. Research students of today need to find a way of tapping the energy resource of the quantum underworld that permeates all space and the starting point for such research that I offer in my book Creation: The Physical Truth  is the explanation of how the sun acquired its spin by interaction with the medium constituting that quantum underworld.
The answer to this question depends upon the physical size of the electron, inasmuch as it is the electron in the hydrogen atom that provides virtually the whole of the atom's reaction cross-section subjected to the sun's radiation pressure. It is a curious fact, however, that a century and more has elapsed since J.J. Thomson discovered the electron and yet we are told, as by Cambridge Encyclopaedia (Cambridge University Press, 2000 Edition, page 908), that the electron "...(has) no known size, (is) assumed point-like, (with) no known substructure.." The wisdom of today's physics community does not therefore allow us to see a way forward in our efforts to comprehend the sun's energy source as being regulated by pressure balance with energy being tapped from the quantum activity of the underworld that pervades all space. We must therefore revert to the wisdom of the past.
The size of the electron can be specified in two ways. Firstly, if we see the electron as a ball of electric charge, that charge has a certain radius. In pre-Einstein times (1904) physics textbook knowledge  gave the formula for charge radius a in terms of the electron mass m and the electron charge e:
The sun's temperature T sets up a radiation pressure (T)4/c, where σ is the Stefan-Boltzmann constant. This is effectively halved when the radiation is intercepted by a spherical form owing to the variation of angle of incidence. For an obstructing spherical object of diameter λ , this implies a force that is:
The relevant numerical data in S.I. units for the terms involved are:
λ = 2.426x10-12, σ = 5,670x10-8, c = 2.998x108, G = 6.673x10-11, M = 1.673x10-27, R = 6.96x108, and ρ = 1.41x103, which is the mass M divided by the cube of twice 5.291x10-11, the Bohr radius applicable to the electron of the hydrogen atom. The temperature T is then evaluated as 5,695 Kelvin.
The solar constant according to physics textbook data  as based on black-body radiation assumptions and use of the Stefan-Boltzmann constant is somewhat uncertain, but, as that reference states:
"... the best available figure is 1.94 calories per sq. cm. per minute (equivalent to 0.135 watts per sq. cm.), giving a temperature of about 5,800 K."
The educational value of this analysis is very considerable. Implicit in that pre-Einstein teaching is the physical basis of the formula E = Mc2, it being the result of the electron exhibiting an inertial property that assures it does not radiate its own electric field energy when accelerated. See Chapter 8 of ref. . This underpins quantum theory. Physics is a school subject giving the foundation for a career concerned with technology, engineering, so why not invite the student to ask how Maxwell's equations allow lateral charge displacement in the space medium with the passage of a wave if there is not something there to provide dynamic balance? That is the key giving the link between matter and something in space, gravitons, which provide that balance and, incidentally, account for gravitational action. See Part I of ref. . Proton creation and the ongoing activity in space seeking to create more protons but failing for lack of the needed angular momentum combine to explain both the amount of matter in our universe and the amount of quasi-matter (dark matter) as explained in Part II of ref. . The problem, of course, is the task of daring to teach physics which questions what Einstein has bequeathed to us, but we face a future of diminishing energy resource if we do not rise to that challenge and cannot afford to ignore what I claim to be the verifiable truth that governs the physics concerned with the creation of matter and the necessary energy source involved. Furthermore, given the dangers associated with nuclear energy, it is sensible to direct the student mind towards an alternative source of energy, one which allows the student to form a physical picture of the energy underworld and verify it by checking the mathematical analysis that underpins what I have presented.References
P.S. As a final note, may I say that I just cannot understand how any physicist can have missed seeing the fact that, if the sun is composed of hydrogen atoms and is ionised, as must be so given its temperature, then the protons that are freed will be pulled together by gravity sufficiently to cause it to have a positively charged core. That prevents further gravitational compaction and precludes conditions within the sun that are deemed to sustain nuclear fusion. The Large Hadron Collider (LHC) under construction at CERN, in serving to bring protons into collision in spite of their mutual repulsion cannot possibly, therefore, tell us anything that relates to the natural phenomena evident in the stellar matter that constitutes our universe. As to non-stellar matter, such as is found in planetary matter, meaning heavy atoms or molecules, there is evidence of an associated heavy graviton form having a mass of 93 GeV/c2 but LHC physicists are looking elsewhere and for a slightly heavier imaginary particle (the Higgs particle).