Original: Neptunium (named for the planet Neptune, the next planet out from Uranus, after which uranium was named) was first discovered by Edwin McMillan and Philip H. Abelson in the year 1940 in Berkeley, California.
Simplified: It is named after the planet Neptune in the same way as Uranium is named after the planet Uranus. Neptunium was discovered in the year of 1940 by two men named Edwin McMillan and Phillip H. Abelson.