Greek mythology in popular culture elements tantalum and niobium are always found together in nature, and have been named after the King Tantalus and his daughter Niobe. The element promethium also draws its name from Greek mythology, as does titanium, which was named after the titans who in mythology were locked away far underground, which reflected the difficulty of extracting titanium from ore. The U.S. Apollo Space Program to take astronauts to the moon, was named after Apollo, based the god's ability as an archer to hit his target and being the god of light and knowledge. Oceanographer Jacques-Yves Cousteau named his research ship, a
Greek mythology Nereids (who inhabited the sea), river gods, Satyrs, and others. In addition, there were the dark powers of the underworld, such as the Erinyes (or Furies), said to pursue those guilty of crimes against blood-relatives. In order to honor the Ancient Greek pantheon, poets composed the Homeric Hymns (a group of thirty-three songs). Gregory Nagy regards "the larger Homeric Hymns as simple preludes (compared with "Theogony"), each of which invokes one god". The gods of Greek mythology are described as having essentially corporeal but ideal bodies. According to Walter Burkert, the defining characteristic of Greek anthropomorphism is that "the Greek