Lunation

A lunation is the Moon's monthly circuit relative to the Sun: New Moon when the two conjoin, first quarter when the Moon pulls ninety degrees ahead, Full Moon at opposition, last quarter at the closing square. The phases are simply aspects between the two lights, which is why the vocabulary of aspects and the vocabulary of the month rhyme.

In practice, lunations are astrology's fine-grained timer. Each New Moon opens a roughly month-long chapter, colored by its sign and, in your own chart, by the house where it lands; the Full Moon two weeks later brings that chapter to full visibility. A lunation falling exactly on a natal planet is a respectable way to pick out the month when a slower transit finally gets triggered.

A lunation that occurs near the lunar nodes is an eclipse, the amplified version of the same event.