Cusp — Astrology glossary

A cusp is a boundary line in a chart. Most often it refers to the starting edge of a house, but the term also describes the point where one zodiac sign ends and the next begins. Astrologers use house cusps to determine which sign rules each area of life and where planets fall. It matters because a planet sitting near a cusp can be read as belonging partly to the next house or sign, which affects interpretation. For example, someone born when the Sun is at the very end of Aries, just before it crosses into Taurus, is sometimes loosely said to be on the cusp; strictly, the Sun is still in Aries, but its placement so close to the boundary can blend the two signs' qualities in a reading.