Ayanamsha Principles

Summary: Covering the basic principles and applications of the Ayanamsa (Ayanamsha) which is used to translate planetary positions from the Tropical zodiac into the Sidereal zodiac.

Quick Facts about the Ayanamsha

    • The Tropical Zodiac moves slowly relative to the background of the ‘fixed’ stars [1] and the Sidereal Zodiac does not move at all. So it, and all the signs in it, remain anchored forever against these stars.
    • The Ayanamsha is the angular distance between the starting point of the Tropical zodiac and the starting point of the Sidereal zodiac. Currently it is around 24 degrees.
    • Sidereal Position = Tropical Position – Ayanamsha
    • For example: if the Sun is at 29 degrees Virgo in the Tropical zodiac it will now be located at 29 – 24 deg. = 5 deg. Virgo in the Sidereal zodiac. However, if it lies between 0 deg. and 24 deg. in Virgo in the Tropical zodiac it will now be in Leo in the Sidereal zodiac. It has moved ‘backwards’ by the Ayanamsha amount. Suppose the Sun was at 20 degrees Tropical. This is equal to Sun at 20 – 24 = – 4 degrees from Virgo sidereal. This means it has moved backwards into the sign before it, so is now at 30 – 4 = 26 degrees Leo.
    • The Ayanamsha is important. It enables the position of the planets (as calculated by astronomers) to be accurately placed in their correct signs, houses and Nakshatras in the Sidereal chart. This forms the foundation for accurate predictions.
    • The Ayanamsha used by most professional Vedic astrologers is that calculated by Lahiri (although some astrologers use a small correction factor to ‘fine-tune’ it).
    • Lahiri’s Ayanamsha is also officially recognised by the Indian Government. They have standardised on this Ayanamsha because many (but not all) religious festivals in India are based on the Moon (sometimes both Sun and Moon), its phases and position in the Nakshatras or lunar mansion
    • Because of the astronomical phenomenon known as the ‘precession of the equinoxes’ the Ayanamsha is not a fixed number, but increases slowly with time.
    • If we take Lahiri’s Ayanamsha we find it was about 23 degrees in 1950 (the year I was born) and is now about 24 degrees. So it increases by an average of about 1 deg. every 72 years.
    • At some time in the distant past the two zodiacs were in perfect alignment and coincided exactly . Both then had the same starting point in the sky – estimated to be around 285 AD (if using the Lahiri Ayanamsha).
    • If we are just beginning our studies of Jyotish it is highly recommended we start with Lahiri’s Ayanamsha. This is usually an option (often default) in Vedic astrological software. Lahiri’s Ayanamsha is published in most ephemeris (ephemerides) tables. After we gain more experience we can explore the consequences and results of different Ayanamshas.

Ayanamsa (Ayanamsha) – Basic Principles

The Ayanamsa (pronounced ‘Ayanamsha’) is the angular distance, measured in degrees, between the starting point of the Tropical zodiac (used by most western astrologers) and the starting point of the Sidereal zodiac used by all Vedic astrologers.

So, what is the difference between the two zodiacs? Well, both the Tropical and the Sidereal zodiacs are identical in that both have 12 signs and each sign occupies exactly 30 degrees of the sky (or ‘celestial sphere’). Both also have identical names for the signs e.g. Aries, Taurus, Gemini, etc. The only difference between them is where they start in the sky and this difference is called the ‘Ayanamsha’.

The starting point of the Tropical zodiac (astrologers call this ‘zero degrees Aries’) can be measured with very high precision by astronomers and this precise point in the sky then referenced to the very distant ‘fixed’ stars [1] in our own galaxy. This measurement of the Spring (sometimes called ‘Vernal’) Equinox defines the position of zero degrees Aries in the sky. So, the Tropical zodiac is linked to the seasons. Also the signs of this zodiac slowly move through the sky. They don’t stay in the same place when referenced to the distant stars.

The starting point of the Sidereal zodiac cannot be measured directly, but its position can be inferred. It can also be found by ‘reverse engineering’ – by examining real life events matched against birth-chart predictions. Various scholars and academics have arrived at their own figures for the angular distance between the starting points of the Tropical and Sidereal zodiac. Most accepted Ayanamshas are within one or two degrees of each other [3]. Although this doesn’t sound much, it can have a major influence on chart interpretation and predictions if a planet’s position ‘moves’ between signs or houses as a result of different Ayanamshas. It also seriously affects the divisional charts (e.g. ninth divisional chart or ‘Navamsha’ – which is examined for details about marriage and partnerships) used in Jyotish. It can also affect the interpretation of transits too!

The Tropical Zodiac moves against the background stars

If the Spring equinox point always remained in the same location (with reference to the ‘fixed’ background stars) the Ayanamsha concept would be fairly straightforward.

Unfortunately things get more complicated as the starting point of the Tropical zodiac actually moves relative to the background of the ‘fixed’ stars over a period of time. This movement, although small (e.g. an average of about 1 degree per 72 years), is caused by the astronomically observable ‘precession of the equinox’ phenomenon [2].

To further complicate things, the rate of movement of the equinox point itself varies over a period of time. This is due to complex gravitational interactions between the Earth, Sun, Moon, Jupiter, etc. in our solar system. So the figure of 1 degree per 72 years is just an average. Complex astronomical algorithms can compute a more accurate figure over long periods of time.

Footnotes

[1] The ‘fixed stars’ are so far away from earth that their angular motion relative to our sun is extremely small, even over many thousands of years. So we can legitimately use the term ‘fixed’ or ‘immovable’.

[2] The equinox point on the Earth’s orbit around the sun moves, relative to the background of the ‘fixed’ stars, due to what is called the ‘precession of the equinox’. This is a well-defined astronomical phenomenon which is due to a slight ‘wobble’ on the Earth’s axis of spin.  The wobble is caused by gravitational forces from Sun and Moon that act on the bulge at the equator (as the rotating earth is not a perfect sphere due to ‘centrifugal’ forces) . It is a bit like a child’s spinning top or toy gyroscope that wobbles – the top spins rapidly about the central axis of spin, but the axis itself slowly rotates and  traces out a conical shape. The Earth takes around 26,000 years to complete 1 precessional cycle (calculated using present rate of precession).

[3] Ayanamshas Compared. The following, frequently quoted  figures were calculated by an online Ayanamsha tool  for the 1st January 2024:

Raman Ayananmsha: 22 deg 44 mins

KP Ayanamsha: 24 deg 06 mins

Lahiri Ayanamsha: 24 deg 11 mins

Fagan-Bradley Ayanamsha:  25 deg 04 mins

Note the very close agreement between the Lahiri calculation and that of KP (Krishnamurti Paddhati system). The Fagan-Bradley figure is not used by Jyotish Astrologers, as it was intended for Western  Astrologers using the Sidereal Zodiac.


Additional Information on Vedic Astrology

Introduction to Jyotish. A range of articles for people entirely new to Vedic Astrology. Including: Introduction, FAQs, Origins and Karmic Implications.

Key Concepts in Jyotish. Articles covering the Sidereal Zodiac, Planetary Forces, Forecasting Analogies and ‘Planetary Antidotes’.

For Western Astrologers. Articles examining major differences between the two systems and the paradigm shift needed by Western Astrologers wanting to understand the subject.

Learn Jyotish. An extensive collection of articles covering key facts, concepts and methods. Aimed at ‘foundation level’ students. Includes essential information needed before beginning chart interpretations. Covering: Chart Formats, Planets, Houses, Mahadasha Periods, Transits, Aspects, Birth-time Errors, Natural and Functional Benefics / Malefics, Chart Interpretation Basics, etc.