Twelve slices
of one circle.

Why there are twelve

The Sun takes a year to return to the same point against the background sky. Divide that circle into twelve equal parts and each one takes about a month — which is roughly a lunation, and that is almost certainly why twelve rather than ten or sixteen. The division is Babylonian, it is at least two and a half thousand years old, and it is arithmetic rather than observation: every sign is exactly thirty degrees, regardless of how much sky the constellation of the same name actually occupies.

That last point is where most confusion starts. The constellation Virgo sprawls across more than forty degrees of the ecliptic; the constellation Scorpius is clipped to about seven. The signs are all thirty. They are two different systems that were briefly aligned and have not been for two thousand years — which is a story worth reading in full.

The three properties

Each sign is defined by three things, and the way they interlock is the actual engineering of the zodiac.

• Element — fire, earth, air or water. Four elements, three signs each, spaced 120° apart. Signs sharing an element always stand at a trine to one another.
• Mode — cardinal, fixed or mutable: whether the sign starts, holds or adapts. Three modes, four signs each, spaced 90° apart.
• Ruler — the planet the sign answers to. Before the telescope there were seven visible bodies for twelve signs, so five planets ruled two signs each; Uranus, Neptune and Pluto were assigned later, and both readings are still in use.

Because element and mode are both fixed functions of position on the wheel, no two signs share both. That is not a coincidence — it is the constraint the whole scheme was built to satisfy. The elements and modes are set out here, with the grid that shows why.

Every sign, side by side

What a sign is not

A Sun sign is one placement in a chart that has a dozen. It says where the Sun was on a particular day, and nothing at all about where the Moon was, what was rising, or what angles the planets stood at. Two people born the same week can share a Sun sign and have almost nothing else in common on paper.

That is not a criticism of Sun signs — they are a genuine and very old part of the tradition. It is an argument for not stopping there. The moon phase you were born under is a second light with its own reading; the sidereal system answers the same question from a different zero; the Chinese zodiac is a different scheme entirely. Where this site stops, and what a full birth chart would add, is set out on the method page.

The three faces of each sign

Every sign is split into three ten-degree faces. The first answers to the sign itself, and the other two answer to the next two signs of the same element. The face you were born in changes the tone of the sign, not the sign itself. All thirty-six faces are on their own page.

The sign and its constellation

A sign is a slice of the Sun's path, and a constellation is a pattern of stars. The two were laid over each other about two thousand years ago and have been drifting apart ever since, because the Earth's axis wobbles slowly. Each sign page shows its constellation as it is drawn on a star chart, and the precession page gives the full account.

Reading one sign beside another

The pairing tool on the home page works from the angle between two signs rather than from a table of matches. The angle is a number of degrees, and the seven aspects page says what each one means.

What these pages do not claim

Nothing on the sign pages is medical, psychological, legal, financial or safety advice, and none of it should be used to make a decision about another person's character. The method page lists what is computed and what is only assigned by tradition.