Period 5 element and because of its rarity, rhodium is usually alloyed with platinum or palladium and applied in high-temperature and corrosion-resistive coatings. White gold is often plated with a thin rhodium layer to improve its optical impression while sterling silver is often rhodium plated for tarnish resistance. Rhodium detectors are used in nuclear reactors to measure the neutron flux level. Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named
Planets in astrology correspond to the elements known to the ancients—air (Uranus, god of the heavens), water (Neptune, god of the sea), and fire (Pluto, god of the underworld)—which leaves the elements earth and ether (the fifth element of the fiery upper air). In other words, it is claimed that the two planets to be discovered will be named after an earth god or goddess (such as the Horae), and after Aether, the Roman and Greek god of the upper air and stars. In Western astrology, the symbolism associated with the planets also relates to the zodiac signs and houses of the horoscope