Blackbody Radiation Explorer

The emission spectrum of a blackbody is unequivocally determined by Planck's law of radiation. As thermal energy increases, the peak wavelength shifts predictably according to Wien's displacement law, λ_max = b/T. This interactive model demonstrates the non-linear relationship between temperature and spectral density. The strictly defined probability distribution of photon emission represents the absolute thermal limit of macroscopic objects in thermal equilibrium.

Anything above absolute zero radiates light, and this tool shows the one rule behind it: the shape of a blackbody's spectrum depends only on its temperature, never on what it is made of. A lump of iron and a distant star at the same temperature emit exactly the same curve. The practical takeaway is that color is a thermometer — slide from red-hot to blue-white and you are reading temperature straight off the glow.

The most flawless blackbody ever measured sits in no laboratory — it is the whole sky. The cosmic microwave background, left over from about 380,000 years after the Big Bang, matches a Planck spectrum at T = 2.725 K to better than 0.01%, peaking near 1.06×10⁻³ m in the microwave range. NASA's FIRAS instrument found no deviation larger than a few parts in 10⁵, making cosmology's oldest light also physics' cleanest thermal curve.