What a birth chart is

A birth chart is a map of where the Sun, Moon and planets were in the sky at one moment, seen from one place. A date, a time and a place go in. A position for every body comes out.

The positions come from an ephemeris, a table of computed sky positions. You can check any of them against another ephemeris, and each lesson says where an answer depends on a choice. The result is a snapshot: the same sky seen from another city, or an hour later, gives a different chart.

The chart is drawn as a chart wheel. The outer ring is the zodiac, twelve signs of 30° each. The bodies sit inside it, each at the position it held. The houses divide the inside, and the lines across the middle are aspects.

Pick a layer below. It is drawn at full strength and the rest is dimmed, not hidden, so you can see where it sits in the whole.

A chart records positions. What a position means is the work of a tradition, and traditions disagree: Hellenistic astrologers read a chart differently from modern psychological ones.

These lessons keep the two apart. The first two cover the sky. The next seven build the vocabulary, one idea each. The last three test how far to trust it. Nothing here predicts anything, and what astrology can and cannot tell you says so in full.