syzygy

The alignment of three celestial bodies in a straight line — most commonly the Sun, Earth, and Moon. Syzygies produce eclipses (when the Moon is between Sun and Earth, or Earth is between Sun and Moon) and the extreme spring tides that occur at new and full moons. The word is also, quietly, one of the best words in the English language — three syllables, no standard vowel, and a meaning that is perfectly precise.