Re: [Phys-L] Sunlight Brighter Than The Sun???

[brian whatcott <betwys1@sbcglobal.net>]

Solar coronal temperature is 1E6 K plus.

Pasachoff at Williams, writes:
"Basically, one cannot account for the heating of the corona by a 
radiative flow, so we think the corona is heated by some sort of 
magnetohydrodynamic (MHD) wave flowing out of lower levels of the sun. 
Images of the sun in the far ultraviolet and in X-rays (acquired most 
recently by the Solar and Heliospheric Observatory 
spacecraft<http://www.scientificamerican.com/topic.cfm?id=spacecraft>, 
the Yohkoh satellite, and the NIXT rockets) show that the heating of the 
corona is localized in solar active regions, which indicates the 
important role played by the magnetic field. There are perhaps a dozen 
specific models that have been proposed to account for the high 
temperature of the corona. These models involve fast-mode MHD waves, 
slow-mode MHD waves, Alfven waves, et cetera. The older idea that 
acoustic waves flowing out of lower levels heats the corona was 
abandoned in the 1970s, when the Orbiting Solar Observatory 8 spacecraft 
did not see such waves in the chromosphere, the layer just above the 
photosphere (the apparent 'surface' of the sun in visible light). It 
remains possible, however, that some acoustic waves can be formed at 
higher levels. "

"nieve" (Br. dialectical) fist, "nieve/nevar"  snow, "naive/naif" ingenuous.

Brian Whatcott   Altus OK


On 8/14/2013 9:43 AM, Chuck Britton wrote:
> 'Temperature' is not a trivial concept.
>
> and I suspect that this statement of the 2ndLoT is a bit nieve for this reason.
>
>
> On Aug 14, 2013, at 10:22 AM, "Folkerts, Timothy J" <FolkertsT@bartonccc.edu> wrote:
>
> > OK ... a few more numbers
> >
> > 5780 K = surface temperature of sun
> > 63.3 MW/m^2 = thermal radiation from surface of sun from Stefan Boltzmann
> >
> > 46,400 = (1 AU/radius of sun)^2
> > 1360 W/m^2 = (63.3 MW/m^2) / 46,400 = solar insolation at earth (top of atmosphere)
> >
> > (1000 W/m^2 = approximate solar power flux at surface)
> >
> >
> > So a plane surface facing the sun at noon would receive about 1 kW/m^2.  With a single plane mirror you could approximately double this number to 2 kW/m^2 by re-directing light that would have fallen somewhere else.  Add another mirror and you are up to 3 kW.   Change to a parabolic mirror and you could make this many times larger.
> >
> > The question is "what it the maximum possible amount of sunlight you could focus onto a surface?"  I would conclude that the maximum would occur when sunlight is focused from every possible direction so the surface "sees" the sun in every direction.  Then the temperature of the surface would rise toward the temperature of the sun (radiative equilibrium).  I.e. you get 46,600x the solar insolation = 63.3 MW/m^2.
> >
> > The paper seems to claim 72 MW/m^2 for the focused sunlight, which would drive a blackbody absorber to a temperature HIGHER than the temperature of the sun = heat flowing from a cooler object to a warmer object!
> >
> >
> >
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