ayanamsa
An ayanamsa is a correction factor used in Hindu astrology, also known as Jyotisha. It accounts for the precession of the equinoxes, a slow, gradual shift in the Earth's rotational axis that causes the position of the vernal equinox to move westward relative to the fixed stars. Over long periods, this shift causes the tropical zodiac, which is based on the seasons, to drift apart from the sidereal zodiac, which is based on the constellations.
There are several different ayanamsas used in Hindu astrology, each calculated based on different historical observations