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 subterranean house of Hades and his predecessors, home of the dead. Influences from other cultures always afforded new themes. According to Classical-era mythology, after the overthrow of the Titans, the new pantheon of gods and goddesses was confirmed. Among the principal Greek gods were the Olympians, residing on Mount Olympus under the eye of Zeus. (The limitation of their number to twelve seems to have been a comparatively modern idea.) Besides the Olympians, the Greeks worshipped various gods of the countryside, the satyr-god Pan, Nymphs (spirits of rivers), Naiads (who dwelled in springs), Dryads (who were spirits of the trees),