Key Concepts

• • Wien's displacement law: λ_peak = 2.898×10⁶/T nm — hotter objects peak at shorter wavelengths
• • The Sun (~5778 K) peaks in visible light; cooler stars appear red, hotter appear blue-white
• • Stefan-Boltzmann law: total power L ∝ T⁴ — tiny increases in T cause huge increases in luminosity
• • Planck's law resolved the "ultraviolet catastrophe" (classical physics predicted infinite UV output)
• • Cosmic microwave background (2.7 K) peaks in the microwave region at ~1 mm