Cerium was discovered in 1803, independently by Jons Jacob Berzelius and Wilhelm Hisinger in Sweden and by Martin Heinrich Klaproth in Germany. It was named after the asteroid Ceres, which the astronomer Giuseppe Piazzi had discovered only two years before, in 1801. Cerium is a soft, silvery, reactive metal, the most abundant of all the rare earths, used in catalytic converters, in polishing powders and in the misch-metal alloy of lighter flints. Cerium shifts readily between two oxidation states, which makes it a valuable catalyst, notably in self-cleaning oven coatings and vehicle exhaust converters, and its oxide is the standard fine abrasive for polishing glass and precision optics.
Cerium mischmetal's pyrophoric spark, the same effect that makes lighter flints work, was also exploited in tracer ammunition and aircraft countermeasure flares during the twentieth century, extending a mundane pocket-lighter mechanism into a genuine military technology. Cerium oxide additionally serves as a UV-blocking component in some glass and ceramic glazes, and it was one of the earliest rare-earth compounds put to industrial use, decades before most of its lanthanide neighbours found any application at all.