SED deviation from Black Body - real objects

[Nereid]

You heat an ideal material (solid, liquid, gas) and it emits electromagnetic radiation, with a spectral energy distribution (SED) following that of a "black body", per Planck.

You heat a homogeneous real material (a lump of iron, a body of water, some hydrogen; things like dust with a wide range of sizes suspended in a gas of mixed composition have their own complications) and the SED deviates from Planck.

To what extent can these deviations be estimated, from a modest set of input parameters (derivable 'from first principles'?)? How broad is the range of applicability of these estimates (e.g. SED BB deviations to the 10%/1%/ppm level? state of matter? composition? temperature?)? I'm assuming thermodynamic equilibrium, etc. In what circumstances is it necessary to resort to 'brute observation' (measure the SED), as a priori estimation is known to be 'wrong' (or, more likely, able to reliably estimate only wide ranges)?

And what happens when you have a plasma?

 

[Aaron Barnard]

Is there a simple set of parameters that can be used to estimate the SED in this case?

The answer to your question depends on the complexity of the material, its composition, and the temperature. Generally speaking, if the material is homogeneous and its composition is known, then it is possible to estimate the SED deviations from Planck's law to a certain degree. This estimation can be done using theoretical models or numerical simulations. The accuracy of the estimation will depend on how well the material properties (such as absorption coefficients, emission coefficients, etc.) are known.

If the material is composed of multiple components with varying temperatures, it is more difficult to accurately estimate the SED deviations. In this case, it may be necessary to rely on brute observation to obtain accurate SED data.

When dealing with plasmas, the SED can be estimated by taking into account the various components of the plasma (electrons, ions, atoms, molecules, etc.). The SED can also be estimated using numerical simulations, which take into account the interactions between the particles in the plasma. However, the accuracy of these estimates can vary depending on the accuracy of the data used to build the models.

 

[charng]

The deviations in the SED from a black body can be estimated to a certain extent using input parameters such as temperature, state of matter, composition, and size distribution. These parameters can be derived from first principles, such as thermodynamic equations and material properties. However, the accuracy of these estimates may vary depending on the complexity of the material and the precision of the input parameters.

The range of applicability of these estimates also depends on the level of deviation being considered. At a larger scale, such as the 10% or 1% level, these estimates may be more reliable and applicable to a wider range of materials. However, at smaller scales, such as the ppm level, the deviations may be more difficult to estimate accurately and may only be applicable to a limited range of materials.

In certain circumstances, it may be necessary to rely on "brute observation" to measure the SED of a real material, particularly when the deviations from a black body are expected to be significant. This could be due to the complexity of the material or the limitations of the input parameters used in the estimation.

When dealing with a plasma, the deviations from a black body can be even more significant. This is because plasmas are highly ionized and have a wide range of energy levels, resulting in a complex SED that cannot be accurately estimated using simple input parameters. In these cases, brute observation is often necessary to determine the SED of the plasma.

Overall, the estimation of SED deviations from a black body is a complex task that requires a thorough understanding of the material and its properties. While some estimates can be derived from first principles, the accuracy and applicability of these estimates may vary depending on the specific circumstances. In cases where accuracy is critical, brute observation may be the most reliable method for determining the SED of a real material.