Its Parts and How They Fit Together

A birth chart in this tradition is a map of the sky at a moment of time, and its meaning is read from how the parts combine. The signs divide the ecliptic into twelve equal arcs; the houses divide the local sky by the daily rotation of the earth; the planets are placed in both, and the aspects measure the angles between them. Finer divisions (the thirty-six decans, the individual fixed stars, the calculated Arabic parts and the degree-by-degree Sabian symbols), are overlaid on that frame.

This section treats the tropical, equinox-based zodiac of the Western tradition. The sidereal, star-based astrology of India is a separate system with its own logic and is gathered under Vedic Astrology, and the Chinese and East Asian systems under Eastern Systems.