Sidereal vs tropical zodiac: why your sign changes

Both zodiacs divide the ecliptic — the Sun's apparent path — into twelve 30° signs. They differ only in where 0° Aries is anchored.

The tropical zodiac (Western astrology) anchors 0° Aries to the March equinox: the moment the Sun crosses the celestial equator northward. The sidereal zodiac (vedic astrology) anchors the signs to the fixed stars.

These two frames drift apart by about 1° every 72 years because Earth's axis precesses — a 26,000-year wobble that slides the equinox backward through the constellations. The accumulated gap is the ayanamsa, currently about 24° (Lahiri ayanamsa, the Indian government standard). That is why a tropical Taurus Moon can be a sidereal Aries Moon: same Moon, same sky, two coordinate systems.

Neither is "wrong." Tropical astrology reads the seasons; sidereal reads the stars. starscore computes both for every chart — try it in the birth chart calculator — and the nakshatras are always sidereal.

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