Gold is a chemical element with the symbol Au and an atomic number of 79. It has a low refractive index in the visible region but high absorption (k) especially in the near-infrared region. Because of its high-reflectivity in the near-infrared it is used for the protective coatings on many artificial satellites, in protective faceplates in thermal protection suits and astronauts' helmets, and also for electronic warfare. Gold is a dense, soft, and shiny metal and the most malleable and ductile of pure metals. A gram of gold can be stretched out into a square meter of area, beating it so that it is thin enough to become translucent. Light that passes through the translucent gold will appear greenish-blue because gold reflects yellow (570-580 nanometers), orange (585-620 nanometers), and red light (630-740 nanometers). You can see the rapid change in refractive index and absorption in the graphs below. Because of its resistance to oxidation gold can be used as an optical standard or reference material in a series of spectroscopic measurements.
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