Graphical view of Planck's law for a black body (an ideal absorber and emitter). Planck's law states that any body that has a temperature above absolute zero emits electromagnetic radiation at all wavelengths. We can use Planck's law to predict the temperature of a remote body without actually being there, but seeing how much radiance is emitted by it on the spectrum we're scanning on. That's friggin awesome!
Objects that are smaller than the wavelength of thermal radiation cannot radiate heat efficiently. A generalized theory of thermal radiation has now been experimentally confirmed at the level of a single object at the Vienna ...
Predictions of the amount of thermal radiation of different frequencies emitted by a body. Correct values predicted by Planck's law (green) contrasted against the classical values (Rayleigh–Jeans law, red and Wien approximation, blue).
Classical physics (Rayleigh–Jeans law, black line) failed to explain black body radiation – the so-called ultraviolet catastrophe. The quantum description (Planck's law, colored lines) is said to be modern physics.
Sun and Earth's emission spectrum: Sun's is 3000/6000 = 0.5 micrometer wavelength (using Wien's Law); Earth's is 3000/288 = 10.41 micrometer wavelength; Sun and Earth are approximately black body radiators (snow is in the infrared); energy emission rate is given by: Stefan-Boltzman law (total emission), Wien's Law (peak emission wavelength), Planck's law (wavelength dependent emission)