Sidereal and tropical zodiac

There are two zodiacs, and today they lie about 24 degrees apart. Anyone with the Sun in Aries in the Western zodiac usually has it in Pisces in the sidereal one. The dispute is old, often badly conducted, and on the merits it cannot be settled — but it can be understood perfectly well.

Where the shift comes from

From precession: the Earth’s axis turns like a spinning top, with a period of about 25,800 years. That carries the spring equinox — the point where the celestial equator crosses the ecliptic — slowly backwards through the constellations, about one degree in 72 years.

About two thousand years ago the two zodiacs coincided. They have been drifting apart ever since.

What each one measures

The tropical zodiac puts zero degrees Aries on the spring equinox. It is tied to the seasons: zero degrees Aries is always the start of spring, zero degrees Cancer always the summer solstice. It measures the relation of the Earth to the Sun.

The sidereal zodiac fixes zero degrees Aries on a fixed star. It is tied to the stars and follows them. It measures the relation to the background of stars.

Both are arithmetically sound. They simply measure different things — like height above sea level and height above ground.

Why the question cannot be settled

Because the answer depends on what the meaning of a sign is grounded in.

If it is grounded in the season — Aries as the opening of spring, hot and dry, pressing forward — then the tropical zodiac is the right one, and the whole doctrine of the four primary qualities hangs on it.

If it is grounded in the constellations themselves, then the sidereal one is right.

The Western tradition settled on the seasons, and settled early: Ptolemy argues the case explicitly. The Indian tradition settled on the stars. Both have remained internally consistent ever since.

The ayanamsa

The distance between the two is called the ayanamsa. Today it is about 24 degrees, and — this is the awkward part — its exact value depends on which zero point is chosen against the stars. Several are in use, and they lie several degrees apart.

Within sidereal practice, then, the question is not finally settled. Anyone calculating sidereally should state which ayanamsa.

The usual misunderstanding

“Astrologers get the arithmetic wrong, because on 1 April the Sun is not in the constellation of Aries at all.”

That is true, and it misses the point. Western astrology claims nothing about constellations: its signs are sections of thirty degrees each, counted from the spring equinox, and they carry the names of the constellations for historical reasons only. This has been known since antiquity and is expressly taught that way.