> Real world materials are rarely ideal black bodies (or ideal reflectors). That's true, but it's also true that all objects eventually reach thermal equilibri

> Real world materials are rarely ideal black bodies (or ideal reflectors). That's true, but it's also true that all objects eventually reach thermal equilibrium with their surroundings. Were this not the case, it would violate the law of energy conservation, and that's a law that's never broken. In that sense, most objects, solids and plasmas in particular, are reasonable black bodies once they achieve equilibrium. Some of them show spectral lines -- emission, absorption or both -- but in most cases those lines appear on top of a blackbody curve. The sun, for example -- perhaps surprisingly, it exhibits a classic blackbody spectrum appropriate to its surface temperature, with many spectral lines contributed primarily by its comparatively low-pressure atmosphere (http://commons.wikimedia.org/wiki/File:Solar_Spectrum.png http://commons.wikimedia.org/wiki/File:Solar_Spectrum.png). The state of matter least like a black body is a low-pressure molecular cloud in space, which often shows only emission and absorption lines, no classic blackbody curve. The lowest pressure gases show the narrowest spectral lines, which is how we can estimate the pressure of a remote cloud of gas illuminated by distant energy sources.