The question was in regard to your assertion:
That is obviously wrong. For example the cosmic microwave background radiation definitely has a "true" blackbody spectrum and was never emitted by a solid object.
Actually you dont know where the CMB came from. It's only theorized as part of the Big Bang model.
From Wiki.....
"Second, in 1987 a Japanese-American team led by Andrew Lange and Paul Richards of UC Berkeley and Toshio Matsumoto of Nagoya University made an announcement that CMB was not that of a true black body. In a sounding rocket experiment, they detected an excess brightness at 0.5 and 0.7 mm wavelengths.
With these developments serving as a backdrop to COBE’s mission, scientists eagerly awaited results from FIRAS.
The results of FIRAS were startling in that they showed a perfect fit of the CMB and the theoretical curve for a black body at a temperature of 2.7 K, thus proving the Berkeley-Nagoya results erroneous.
FIRAS measurements were made by measuring the spectral difference between a 7° patch of the sky against an internal black body. The interferometer in FIRAS covered between 2 and 95 cm−1 in two bands separated at 20 cm−1. There are two scan lengths (short and long) and two scan speeds (fast and slow) for a total of four different scan modes. The data were collected over a ten month period."
But thats not the end of the story there.
From:
COBE and WMAP: Signal Analysis by Fact or Fiction?
"Furthermore, “In the end, the FIRAS team transfers the error from the spectrum of interest into the calibration file” ... “Using this approach it would be possible, in principle, to attain no deviations whatever from the perfect theoretical blackbody. Given enough degrees of freedom and computing power, errors begin to lose physical meaning. The calibration file became a repository for everything that did not work for FIRAS” [8]."
http://www.sjcrothers.plasmaresources.com/COBEwmap-3.pdf
I think the Japanese team should go back and repeat their experiment.
Free electrons have a range of energies. When they combine with H+ to form H or with H to form H-, broad specrum light is emitted. That is one reason why the spectrum of light from the Sun is not described by
Kirchhoff's Three Laws of Spectroscopy (defined before the discovery of electrons).
Another reason is obvious:
There is no solid body emitting the light because the Sun has a temperature of ~5700 K at the top of the photosphere, ~9400 K inside the photosphere and even hotter further in.
I might also ask you what distinguishes a "true" blackbody spectrum from a "false" blackbody spectrum

.
Mainstreams conceptualization of a blackbody based on Kirchoffs experiments are not completely correct.
The blackest material in the world is a solid and reflects .01% of its light.
It is not a perfect blackbody. So its entirely possible that a true perfect blackbody does not exist. And you would have a really hard time convincing me a plasma made a blackbody spectrum.
However, a solid surface sphere will have a spectrum that is much closer to a blackbody than a decreasing density plasma sphere.
Not even galaxies are black bodies and they are much thicker than our suns photosphere.
Thermal Emission as a Test for Hidden Nuclei in Nearby Radio Galaxies
http://www.adsabs.harvard.edu/abs/2004ApJ...602..116W
An Analysis of Universality in Blackbody Radiation
He had initially observed that all materials in his laboratory displayed distinct emission spectra.
Generally, these were not blackbody in appearance and were not simply related to temperature changes. Graphite, however, was an anomaly, both for the smoothness of its spectrum and for its ability to simply disclose its temperature. Eventually, graphite’s behavior became the basis of the laws of Stefan [7], Wien [8] and Planck [3]. For completeness, the experimental basis for universality is recalled [1,2,5,6]. Kirchhoff first set forth to manufacture a box from graphite plates. This enclosure was a near perfect absorber of light (e =1, k =1). The box had a small hole, through which radiation escaped. Kirchhoff placed various objects in this device. The box would act as a transformer of light [6]. From the graphitic light emitted, Kirchhoff was able to gather the temperature of the enclosed object once thermal equilibrium had been achieved. A powerful device had been constructed to ascertain the temperature of any object. However, this scenario was strictly dependent on the use of graphite.
Kirchhoff then sought to extend his findings [1,2,5]. He constructed a second box from metal, but this time the enclosure had perfectly reflecting walls (e =0, k =0). Under this second scenario, Kirchhoff was never able to reproduce the results he had obtained with the graphite box. No matter how long he waited, the emitted spectrum was always dominated by the object enclosed in the metallic box. The second condition was unable to produce the desired spectrum.
http://arxiv.org/ftp/physics/papers/0507/0507007.pdf
[1] G. Kirchhoff, "Ueber den Zusammenhang von Emission und Absorption von Licht und Warme,"
Monatsberichte der Akademie der Wissenschaften zu Berlin, sessions of Dec. 1859, pp. 783-787, 1860.
Google translate "On the relation between emission and absorption of light and warmth,"
[2] G. Kirchhoff, "Ueber das Verhaltnis zwischen dem Emissionsvermogen und dem Absorptionsvermogen der Korper fur Warme und Litcht, Annalen der Physik vol. 109, pp. 275-301, 1860.
Google translate ""On the relationship between the Emissionsvermogen and Absorptionsvermogen the body for warmth and Litcht"
On the validity of Kirchhoff's law of thermal emission
http://ieeexplore.ieee.org/Xplore/l...265348.pdf?arnumber=1265348&authDecision=-203
A nitpick: You never cite the experiment Kirchoff did that involved a box. This sounds more like the theoretical considerations that Planck used to derive
Planck's law.
See above.
So do you see why its impossible for the CMB to be perfect?? And why the sun has a solid surface.