What is "ayanamsa"

Ayanamsa (Sanskrit : "movement" + "component"), also ayanabhāga (Sk. bhāga "portion"), is the Sanskrit term in Indian astronomy for the amount of precession. In astrology, this is the longitudinal difference between the Tropical (Sāyana) and Sidereal (Nirayana) zodiacs. In astronomy too, this is the difference between the length of a tropical year (365.2422 rotations of the earth) and a sidereal year (365.2563 rotations) required to complete one orbit relative to the sun (tropical) or stars (sidereal).