Physics
Wien's Displacement Law
Quick fact
Wien's displacement law allows astronomers to determine a star's surface temperature just from its color—our Sun peaks in yellow-green, while hotter blue stars peak in ultraviolet.
Why this is interesting
You've noticed that a hot stove glows red, but a hotter welding torch appears blue-white. Why does color change with temperature?
Read the full explanation
Understanding Wien's Displacement Law
Imagine a perfect absorber and emitter of radiation—a blackbody. When heated, it emits a continuous spectrum of light. The peak, or most intense wavelength, shifts depending on temperature. As temperature increases, the peak moves to shorter wavelengths (from red to blue). This is why a cool star appears red and a hot star appears blue. The law mathematically expresses this: λmax = b / T, where λmax is peak wavelength, T is temperature, and b is Wien's displacement constant.
A deeper explanation
Wien's displacement law arises from Planck's law of blackbody radiation, which describes the spectral distribution. By differentiating Planck's function with respect to wavelength and finding the maximum, one obtains λmax ∝ 1/T. This inverse relationship is not an accident but a direct consequence of quantum mechanics: the energy of photons (E = hc/λ) ties wavelength to energy, and higher temperatures provide more energy, shifting emission to shorter wavelengths. The law is crucial in astrophysics for estimating stellar temperatures, in thermal imaging for identifying heat sources, and in lighting design for predicting color temperature.