Max Planck, The New Science, 1959.

The clearest evidence that the photosphere is comprised of matter in the condensed state lies in the continuous nature and Planckian appearance of the solar spectrum (see figure below).  Gases are unable to provide such an emission spectrum (see The Little Heat Engine).   In fact, a continous thermal spectrum of Planckian appearance is critically dependent on the presence of a lattice structure in the emitting material as previously outlined (see abstract On Planck).   This is exclusively a feature of the condensed state (solids and liquids). The belief that gases were able to produce a Planckian shapped spectrum is an error which has remained in physics for nearly 140 years. In fact, gases are completely unable to generate such spectra as shown by all earthly studies. The erroneous belief that gases were able to emit a continuous spectrum of Planckian appearance was based on the notion by Planck and Kirchhoff that blackbody radiation was universal in nature. In turn, this was based on an incorrect assumption by Kirchhoff as now reviewed in detail (see the abstract On Kirchhoff and the section on Kirchhoff's Law). The sun is unable to follow Kirchhoff's Law due to the lack of enclosure in a perfect absorber. It is also unable to follow Kirchhoff's Law due to the presence of clear convection currents on its surface. As such, it is inappropriate to set a photospheric temperature based on Planckian arguments. This issue has been addressed at length by the author (Robitaille, P-M.L., On the Validity of Kirchhoff's Law of Thermal Emission, Transactions on Plasma Science, Dec 2003).