EMILIO SEGRE VISUAL ARCHIVES / AMERICAN INSTITUTE OF PHYSICS / SCIENCE PHOTO LIBRARY EMILIO SEGRE VISUAL ARCHIVES / AMERICAN INSTITUTE OF PHYSICS / SCIENCE PHOTO LIBRARY
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Secchi's four classes of stellar spectra. The Italian astronomer Angelo Secchi (1818-1878) used a prism to split the light from a star and observe its spectrum. The black lines (absence of light) are due to the absorption of particular wavelengths of light by chemical elements in the outer layers of the stars. Secchi used these lines to classify stars into five groups.
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