Max Planck discovers Planck's law of black-body radiation.

In physics, Planck's law describes the spectral density of electromagnetic radiation emitted by a black body in thermal equilibrium at a given temperature T, when there is no net flow of matter or energy between the body and its environment.

Solar spectrum compared to black-body
Solar spectrum compared to black-body (Source: Wikimedia Commons)
Max Planck by Hugo Erfurth 1938cr - restoration1
Max Planck by Hugo Erfurth 1938cr - restoration1 (Source: Wikimedia Commons)
Max Planck 1878
Max Planck 1878 (Source: Wikimedia Commons)
Planck's law
Planck's law (Source: Wikimedia Commons)

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Sources and further reading: Wikipedia — Planck's law, Max Planck (CC BY-SA). Images: Wikimedia Commons.