Ayanāṁśa · the sidereal offset

The ayanāṁśa is the distance between two zero points. The tropical zodiac begins at the spring equinox; the sidereal zodiac begins from the fixed stars. Because the equinox drifts slowly backward against the stars, a motion called the precession of the equinoxes, the two have pulled apart over the centuries and now stand near twenty-four degrees. The ayanāṁśa is that gap.

Vedic astrology works in the sidereal zodiac, so a tropical position is converted by subtracting the ayanāṁśa. A planet at 10° tropical Leo, with an ayanāṁśa of 24°, sits near 16° sidereal Cancer. This subtraction is what separates a Vedic chart from a Western one cast for the same moment.

Same sky, two zero points; the ayanāṁśa is the distance between them.

There is no single agreed value. The offset depends on which star fixes the sidereal zero, and schools differ: the Lahiri or Chitrapakṣa ayanāṁśa, anchored to the star Chitrā, is the standard in India and most software, while Raman and Krishnamurti set it a little apart. The codex keeps that as a live disagreement, not a settled number.