Vedic astrology

Ayanamsa

Also known as: ayanamshaayanamsha LahiriLahiriLahiri ayanamsaChitrapaksha ayanamsasidereal zodiacsidereal astrologytropical vs siderealprecession of the equinoxesअयनांश

The ayanamsa is the angle between the tropical zodiac, which starts at the spring equinox, and the sidereal zodiac, which is tied to the fixed stars; Vedic astrology subtracts it from planetary positions, and AstroSensus uses the Lahiri ayanamsa, now about 24 degrees.

Astrologers use two zodiacs. The tropical zodiac, used in Western astrology, begins at the point where the Sun stands at the spring equinox and divides the year into twelve equal signs tied to the seasons. The sidereal zodiac, used in Vedic astrology, is anchored to the stars of the constellations. Two thousand years ago the two almost matched. Since then they have drifted apart, and the size of that gap is the ayanamsa. The Sanskrit word combines ayana, movement or course, and amsha, a portion or degree.

The cause is the precession of the equinoxes. The Earth's axis slowly wobbles like a spinning top and completes one turn in about 25,800 years. As a result the equinox point moves backwards against the stars by about 50 seconds of arc each year, or one degree in roughly 72 years. The tropical zodiac moves with the equinox; the sidereal zodiac stays with the stars. Every year, therefore, the ayanamsa grows a little.

Astronomers and astrologers do not agree on the exact year in which the two zodiacs coincided, which is why several ayanamsas exist. The most widely used is Lahiri, also called Chitrapaksha. It places the star Spica, Chitra in Sanskrit, at the start of sidereal Libra. In 1955 the Calendar Reform Committee of the Government of India adopted it for the national almanac, and it has since become the standard of most Indian astrologers. Other systems include Raman, the Krishnamurti ayanamsa used in KP astrology and Fagan Bradley in Western sidereal astrology. The differences between them are usually around one degree.

AstroSensus calculates its Vedic charts with the Lahiri ayanamsa. The positions of the planets, the Lagna and Rahu are first found in the tropical frame and then the ayanamsa for the moment of birth is subtracted. Houses are then counted whole-sign from the sidereal Lagna. Today the Lahiri value is a little over 24 degrees.

The practical effect is easy to see. If the Sun, Moon or another planet sits in roughly the first 24 degrees of a tropical sign, it falls into the previous sign in the sidereal chart. Someone with a tropical Sun at 10 degrees of Leo has a Vedic Sun at about 16 degrees of Cancer. The same shift applies to the Ascendant and the Moon, and so to the nakshatras, Sade Sati dates and dasha periods.

Neither zodiac is a mistake. They answer different questions: the tropical one follows the seasons and the Sun's relationship to the Earth, the sidereal one follows the background of stars. Each tradition has built its own meanings on its own frame, so a Western sign and a Vedic rashi are best read within their own system, not mixed.