Ayanamsa
The angular offset between the tropical and sidereal zodiacs, used to convert Western positions into Vedic ones.
Ayanamsa (literally 'the part of the precession') is the slowly growing angle between the fixed-star (sidereal) zodiac that Vedic astrology uses and the season-based (tropical) zodiac of Western astrology. Because Earth's axis wobbles, the two zodiacs drift apart by about 50 arcseconds a year — roughly one degree every 72 years.
To cast a sidereal chart you subtract the ayanamsa from a planet's tropical longitude. Today the value is around 24 degrees, which is why a Sun that Western astrology calls 'Aries' is usually 'Pisces' in a Vedic chart.
There is no single agreed ayanamsa. The Lahiri (Chitrapaksha) value is the Indian government standard and the most widely used; Raman and Krishnamurti (KP) are common alternatives. The choice shifts every position slightly, so an honest chart always states which ayanamsa it used.
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