Frits Zernike was a Dutch physicist and winner of the Nobel Prize in Physics in 1953 for his invention of the phase-contrast microscope. Zernike's work helped awaken interest in coherence theory, the study of partially coherent light sources. In 1938 he published a simpler derivation of Van Cittert's 1934 theorem on the coherence of radiation from distant sources, now known as the Van Cittert–Zernike theorem.