Oppositional Alignment
Puzzle 18 of City Nicknames Hard Pack
Question is: Oppositional Alignment
and the answer is: SYZYGY
Word Meaning:
SYZYGY — (astronomy, astrology) An alignment of three celestial bodies (for example, the Sun, Earth, and Moon) such that one body is directly between the other two, such as occurs at an eclipse.
Definitions from Wiktionary.