Eumelanin, a form of the pigment melanin, not only determines our skin and eye coloring but also protects us from ultraviolet and other damaging radiation. Now researchers at MIT and other institutions, including Professor Markus Buehler, graduate student Chun-Teh Chen, and colleagues from the MIT Department of Chemistry have discovered exactly how it blocks a broad spectrum of sunlight so effectively. Using first-principles computation and experimental analysis to derive the molecular structure and optical properties of the material, they found that a key source of the broadband absorption is the geometrical arrangement of the constituents, not their chemical characteristics. This work, published in Nature Communications, could potentially lead to the development of synthetic materials with similar light-blocking and other designer optical properties. Read a news release: https://newsoffice.mit.edu/2014/why-eumelanin-such-good-absorber-light-0522