AstrologgerDefinition & classical context
Ayanamsa (Sanskrit: ayana "direction/movement" + aṃśa "portion/degree") is the angular difference between the tropical zodiac (used in Western astrology, anchored to the vernal equinox) and the sidereal zodiac (used in Vedic astrology, anchored to the fixed stars). Because the Earth's axis precesses — completing a full circle approximately every 25,920 years — the vernal equinox slowly drifts backward through the constellations at roughly 50.2 arc-seconds per year. This means that the two zodiacs drift apart over centuries: currently, the sidereal Aries begins approximately 23–24° behind tropical Aries.
To convert a Western (tropical) planetary position to the Vedic (sidereal) position, the astrologer subtracts the ayanamsa from the tropical longitude. For example, if a natal Sun is at 15° tropical Taurus and the ayanamsa is 23°30', the sidereal Sun position is 21°30' Aries. This explains why most people have a different Sun sign in Vedic astrology than in Western astrology.
Several ayanamsa values are in use among Jyotishis. The Lahiri Ayanamsa (adopted as standard by the Government of India's Calendar Reform Committee in 1955) is by far the most widely used in India. The Krishnamurti Ayanamsa (KP system) and the Raman Ayanamsa are also popular in specific lineages. The choice of ayanamsa affects the degree positions of every planet and can shift some planets from one nakshatra or sign to another, making it a foundational parameter in any Vedic chart calculation.
Related terms
- KundliThe Vedic birth chart — a snapshot of the sky at the precise moment and place of birth.
- RashiOne of the 12 zodiac signs in Vedic astrology, each spanning 30° of the sidereal zodiac and governed by a specific planetary lord.
- NakshatraOne of 27 lunar mansions dividing the zodiac into equal 13°20′ segments with distinct mythological and psychological qualities.
- LagnaThe ascendant — the zodiac sign rising on the eastern horizon at the moment of birth, setting the foundation of the entire birth chart.
- GocharPlanetary transit — the current real-time movement of planets through the zodiac and their relationship to natal chart positions.