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Zodiac
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What it is
The zodiac is a belt of sky about eight or nine degrees wide on either side of the ecliptic — the path the Sun appears to trace against the stars over a year. The Moon and the planets never stray far from that path, so the zodiac is, in effect, the road all the moving bodies of a chart travel along.
Astrologers divide that road into twelve equal signs of 30°, from Aries to Pisces, making a circle of 360°. A planet's position is given as a degree within a sign — Venus at 14° Libra, say — which is simply a way of saying how far it lies around the circle from the starting point.
The name comes from the Greek zōidiakos kyklos, "the circle of little animals", because most of the constellations along the Sun's path were pictured as living creatures: a ram, a bull, a crab, a lion, a scorpion, a goat, fishes.
Signs are not constellations
This is the point that confuses people most. The twelve signs are equal 30° slices of a circle, measured from a fixed starting point. The constellations that gave them their names are groups of stars of very different sizes — Virgo sprawls across more than 40° of the ecliptic, Scorpius barely touches it for about 7°, and the modern astronomical boundaries let a thirteenth constellation, Ophiuchus, reach the Sun's path as well.
So "the zodiac" in astrology means the signs, not the star pictures. Where the signs begin is a separate question, and here the traditions part company:
- The tropical zodiac, used by most Western astrologers, starts 0° Aries at the March equinox, so the signs follow the seasons.
- The sidereal zodiac, used in Vedic astrology and by Western siderealists, anchors the signs to the fixed stars.
Because of the slow wobble of the Earth's axis, the two have drifted roughly 24° apart, which is why someone's Sun sign can differ between them. Neither is "the real" zodiac; they answer to different reference points.
How each sign is described
Every sign carries a set of qualities that a reading draws on:
- an element — fire, earth, air or water;
- a mode — cardinal, fixed or mutable;
- a ruling planet, whose domicile it is, and in some signs a planet that is exalted there.
Inside each sign the tradition marks finer divisions: three decans of 10°, and five unequal bounds, each with its own planetary ruler. These sub-rulers feed into a planet's essential dignity.
How it is read
The zodiac is the style layer of a chart. Planets say what kind of drive is at work, houses say where in life it shows up, and the sign a planet stands in is read as the manner in which it tends to act — Mars in Aries quick and direct, Mars in Cancer more guarded and protective. Aspects between planets are also counted in zodiac degrees: a trine is 120° along the circle, a square 90°.
In the tradition
The twelve equal signs were a Babylonian development of roughly the fifth century BCE, which Greek astrologers in Egypt took up and joined to the Ascendant and the houses. Ptolemy, writing in the second century, already defined the signs by the equinoxes and solstices rather than by the stars — the basis of the tropical zodiac most Western astrology still uses.